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Romy,  I have been trying to explain to myself what happened and how I got to it and trying to recreate this wonderful boiling point.
I tried to make a write up of all the steps needed in order to make it happen,  but it is ever so elusive.
I do have notes on the gea I was suing but several changes have been made since then, that I am confident will eventually help me on the way.
Any way I want to share this in case anyone has got to it or part of it so we can find a more  scientific way to make it happen.

Basic guide to advanced audio
Several stages of performance can be observed in a music reproduction system: Perfect resolution, Sphere like soundstage, Harmonizing effect and Boiling point.  These effects are achievable one after the other on your sound system and will help convert a good performance into a moving, even life changing event without having to leave your listening room.  I will try, to the best of my knowledge to describe these points as detailed as possible, trying to keep the thread of what we are talking about, sound reproduction, and not stray into electronics or equipment setting.
Perfect Resolution
The first step of the way to achieve is a Prefect Resolution of the recorded material. This in itself is what this hobby, art form and industry has been all about if we take away the ego buys.
Of course achieving this is no easy task, but a seasoned audiophile should have perfect ability to do so and can get to this point, mostly if we start talking about sound reproduction and stop talking about equipment as an isolated object in a fetishist way.
The first big barrier to cross is to get rid of the big mess and terrible reproduction at the upper bass level.  The most complicated range of music is here, where most instruments have their fundamental frequencies.  This range has to be solved perfectly to bring transparency to the whole spectrum of listening.  Most setups without a specific channel for this frequency sound cluttered and obscure; Imagine there are high and mid frequencies spiking up and down, but  a flat line of some sort at around  300- 200 hz,  sound just doesn’t seem to go past this flat line,  so you get chopped up instruments going up high,  then a big mess at 300 hz,  and then big thumping disconnected bass from 100 hz down,  but it is hard for an instrument to pass that barrier and go cleanly all the way through,  down to the lowest ranges of listening.   Once you get rid of this barrier, instruments just come to life with much more power and punch, even at lower listening levels; this is what brings in that reality feeling!  Bass being totally integrated with the mid range in one sphere like sound. Yes even a violin sounds fuller with a clean response down to 20 hertz.
Even within a perfect resolution there are still levels.  You can get this complete instrument effect, easily with a single driver speaker, and I guess this is why they have so much popularity, but I would not say getting the complete instrument effect will bring in perfect resolution; for this you need to have the frequency extremes perfectly solved and to be able to reproduce more than one instrument.
I will call a Perfect Resolution of a system when you can be able to play a full orchestra at real life volume levels without even a glitch in reproduction, no small distortions anywhere in the spectrum, no saturation of any level not bass dragging around, good dynamics at each and every frequency, with perfect macro and micro detail resolution.
When the instruments sound like real full instruments perfectly delineated and existing in their own space and you can pin point each one of them in the sound stage.
Sphere like Soundstage
Here is where things start getting more complicated, to achieve this you need to measure the response of your system, an RTA is completely necessary if you didn’t have it already. Also you need to have each channel of your speakers independently wired so you can connect and disconnect it and also be able to modify the volume it is playing at.
This ritual I am about to describe will become part of your setting of a system and unluckily needs to be done often, when a new piece of gear is introduced or when the effect starts to wear out.
The first thing to do is disconnect one side of your play back and concentrate on the other.   Disconnect all the drivers and measure only the response of the tweeter. Then disconnect the tweeter and measure just the response of the midrange, the upper bass, and whatever channels you have individually.  Adjust the volume of each one to get the same volume out of every channel.
You will notice when you start getting under 200 hz big bass peaks and valleys in response appear, this is your room playing tricks on you. There is no easy way to fix this, go ahead and push all the EQ buttons you want, you will just kill sound, but do it because it is good to recognize what dead sound is, and because you will of course not believe me when I tell you that all the electronic gear and digital xovers and room equalizers are useless.  Spend as much time and money as you wish.  Eventually you will come to realize that the only solution to the bass room modes is speaker positioning and volume levels of the different channels you have playing under 200 hz, and learning to accept what you cannot change.
After you are done measuring and adjusting both sides your system will sound like shit.
This is where your training and culture play a roll, all those nights at the concert hall, all those piano lessons, the live events you have listened to; all will become part of how your system sounds. The rest of the adjusting has to be done by ear, this is the detail of it and the devil is in the details.
A completely flat system sounds horrible, depending on your room acoustics and your tastes the volume of each channel, either mono or stereo has to be very slightly readjusted, adjustments of half a db are in place, if you need to adjust too much, it means the measuring will be lost and you will need to start the whole process again.
For this we are already talking about a well set up system with no TV in the middle and with the speakers perfectly positioned and equidistant from the sweet spot.
When everything is in place and al the volumes are perfectly set. You will need to check this 2 points that are off in almost every system I have listened too:
Most probably you will need to lower the highs, most tweeters are set with too much volume because of a cultural mistake,  we have learned to listen and enjoy the sparkle on top of the instruments,  like a foam on top of everything,  tweeters don’t need to call the attention of your ear, tweeters need to disappear and form part of the instrument midrange,  they need to fill in the response of the instrument at the higher levels where the midrange driver cannot go,  but don’t ever be present,  this will kill the reality feeling and destroy the sphere like soundstage.
Lower bass say from 50 hz under depending on your channels, will probably be too high. Again we have been taught by the industry that bass is good and that punchy sound is what we need, I have seen subwoofers in good systems dragged all across the Swan Lake. Subwoofers are there to disappear, to never be heard and just complete the instrument´s lower registers, without calling any attention to them.  But also they are there to bring out the shine of an orchestra when the crescendo is in full.  This is where big dynamics of the subwoofers are needed and this is where they usually can’t perform, the horn channels will be jumping up and down but the bass channels won’t be able to keep up, so one is  tempted to raise the volume, do not do it: when the crescendo is over the bass will be ever present.  The problem is not the volume but the poor dynamic response of the bass channel and it should be addressed this way.  I order to fix this you need to either add more bass speakers, more transducer area, or make one of those huge Bass horns.
These two points could be part of a Perfect Resolution, but be certain that if this is not addressed; the Sphere Like soundstage will not appear properly. Somehow miss adjusted channels break through the sphere and pop the bubble.  The sound shall be of an extended midrange without the crisp highs and the ever present lows.
When all this is achieved the sound stage of your system will gradually begin to increase, instruments will be pin pointed in the space and the midrange will acquire a beautiful fullness, a roundness that will keep growing and on certain recordings you will eventually form a Sphere like Soundstage, where the sides of your soundstage will grow so much and the deepness of the soundstage will be so that the instruments are detached perfectly from the speakers and form a sphere right in front of you.
Again there are levels for this and some systems with better gear and more attention to set up will sound better, will give a fuller sphere soundstage with more ease and with better micro detail of the instruments.  Bigger rooms will of course have a bigger soundstage and are capable of withholding higher volume levels.
To get to this point you already need a speaker system that allows each driver to be adjusted independently, and at least a geometric visual time alignment of the drivers is needed, a separate amplifier for the bass is a requirement too, in order to be able to manage bass response. Be clear, if any of these points are missing from your system you will not be able to get the effect.
Harmonizing Effect
This is very difficult to achieve, I have managed to get there just a few times, and if any adjustment or change of gear is introduced in the system, the effect will be lost and you will need to readjust everything.
Things start to get to a point here where recipes are not easy to give and will not even ensure success.  But some basic points must be established that are definitely needed to achieve this.
I have never been able to get the Harmonizing effect without multiamping.   Biamping has already been established as needed for the prior point, being multiamping very useful.  For the harmonizing effect biamping won’t be enough no matter how perfectly set each speaker volume is, you could probably share one amp for two speakers with very similar response,  but one amp per speaker is the best bet.
The minimal adjustment of volume levels for each driver is so perfectly needed that any contraption being Lpads, speaker level volume controls or even wire gauge adjustments will not bring in the response level we need.
Time Alignment is a must.  For this level you need to have each driver of your speaker system, of course wired independently, but also physically detached from the others in order to be able to slide it forward and backwards until it snaps into place.
The ritual described above has to be conducted again, but this time with another purpose in mind: to time align each driver on your speakers.  This process has been described before in some Altec literature and on some expert websites.   You will have to play a tone at the frequency where the driver´s cross over is set at: for example 500hz.  You connect only the 2 drivers we are measuring and invert the cables on one of them. Then play the tone at the crossover point, 500 hz: and you slide the driver you are adjusting until the SPL meter shows a dip in the response at that frequency.  This has to be done on all of the drivers on both sides of your speakers.
Once everything is reconnected and the system is sounding again a seemingly endless micro volume adjustment of each driver is performed while listening to music.  Again your cultural baggage will play the most important roll on deciding which volume to adjust a how much higher or lower.
Brick by brick is layered of micro adjustments until the volume and the tone on each instrument all along its frequency range are set in order to give it a full image.  Place the image of a violin on your head and imagine it is distorted, if the lower registers are too high, the figure of the violin will be distorted on the bottom, with a big flatulent ass.  You have to lower the volume of that driver to give the violin in your head the perfect size, shape and tone.  This has to be done for every instrument in the orchestra.
If your reference recording, the music you are playing in order to set all the volumes right, is a girl with guitar, you will not have a clear vision of the sound of each channel you are trying to adjust and so you will be blind in most frequency ranges.  Try to adjust the shape of a violin drawing if you cannot see parts of it.  This is why our system needs to be able to play a full orchestra and why our reference recording cannot be simpler music.   If there are no instruments playing on each and every frequency range then we have no “visual” reference present in order to adjust the volume on each speaker driver.
That being said I usually play female voices after all the volumes have been readjusted just to check the response with a more familiar sound, but never readjust volumes then.  It should not be needed The voice will sound perfect and jump out at you beautifully.
With every micro level adjustment the Harmonizing Effect will be more and more present and it will be noticeable.   In the beginning of a concert or when the pianissimo is playing with few instruments you will not notice anything different, but when all the instruments come together the sound will vibrate outside the speakers with this beautiful tone in a resonating sphere like soundstage and you will be unable to leave your seating position!
Boiling Point
This is extremely difficult to achieve, I have only got it once by accident and another time by careful approach, and lost it soon after because of unneeded re adjustments.
It is also very difficult to explain if you have never listened to it.  Above is a narration of it I made when I accidentally got it:
Going back at this narration it explains all of the above points I have been achieving one by one in order to eventually start a boiling point.  How it is done, by magically readjusting everything in an already perfectly set up system!
You can have your system on the Harmonizing effect most of the time,  but only on certain recordings and on a given day when maybe the electricity is better and your senses are relaxed the system might begin to explode in such a way.