Quad ESL-63 and low-powered amps; Sun Audio, Atma

Willemj, you raise good points. And by the way I am sure you know much more about audio than I do, so I will not be making many technical arguments here. A couple of points/questions:

1. As you suggested may be the case, I think you and I have different objectives. I want a system that most effectively tricks my brain into thinking I am listening to a real musical performance, regardless of what distortions or equalizations or trickery is employed. Separately, I don't seek neutrality to a recording because so many recordings are not representative of the original event. I don't want to hear recording flaws perfectly,fine in all their  glory. These topics, though,  have sprouted arguments for decades so probably best we don't chase them here, eh?

2. Maybe this question is a less well-worn road, and I ask this because I am interested in the answer,  not because I am baiting or trying to set you up in any way for a punch line :) ... Couldn't two amps of differing architectures but that each measure flat and neutral (however you measure that), playing music in exactly the same system, sound different? I have read a number of times that playing a dynamic music signal is an entirely different game than is playing test signals. Test signal performance may not be entirely predictive of what happens with a dynamic signal. Is this true? And further, could not the interactions with other components cause the otherwise "measured-equal" amps to sound different because they may operate differently into the real-world speaker load, with real music?

@willemj "There have also been subjective evaluations in the shape of blind tests to see if under controled conditions panels of experienced listeners can distinguish properly designed amplifiers from each other (I participated in one). The answer was that these panels could not distinguish them."

About 10 years ago, I shared a room at CES with a most well-respected and liked (including by me) person in the high-end audio business. If I actually revealed him here some would be floored. One thing I’m not crazy about is he likes to go around challenging people in the most (in my opinion) classless of ways by putting a ridiculous amount of $$$ out there if a person can pass a test he runs to distinguish A versus B. I told him lets not get into the conversation because I don’t play such games, especially with friends or people I like, I just don’t have that kind of ego. Bottom line, the faithful production of music in the home is something I love, not something akin to a male parts measuring contest, though so many make it into that. Anyway, to his absolute astonishment, I (easily!) scored 100%.  He dejectedly / puzzledly / worriedly wondered what he needed to go back to the drawing board to tweak

Montaldo, thanks for your friendly response. My aim is what Peter Walker once called 'the closest approach to the original sound'. There are many problems with that, and the two biggest ones are the recording and mastering on the one hand, and the speakers and their in-room response on the other. The former set of problems we can do little about other than vote with our money/feet, the latter you and I have solved to the best of what I at least believe is possible, by using Quad electrostats (plus subwoofer support). In between those two ends of the reproduction chain I want to keep things neutral, and with the designer of our speakers I believe that can be achieved without too much trouble. If you believe or fear a perfect match is hard, just try the current incarnation of your speaker designer's own take at the problem of amplifier design, the Quad QSP or now the Artera. I love my more or less identical 606-2.
Of course there are all kinds of ways in which you can make an amplifier that sounds bad, and there are all kinds of ways in which you can make an amplifier that sounds very sweet but that is not neutral or accurate. And yes, you have to measure in real life situations such as a realistic speaker load. But after all that, it is still quite doable to design amplifiers in different ways, and at the end of the day have them all sound equally neutral. Here, listening tests are of course the final arbiter, but they have to be done under controlled conditions, and as I wrote, I did join one of those blind tests, run by Peter Walker himself, and the result was sobering (I had expected to be able to distinguish the different amplifiers).
By the way, if there is one suggestion I may do, it is to use a DSpeaker Antimode 8033 to tame your subwoofers. I did, and it was the best audio investment of many years, particularly with electrostats.

Funny you mention equalization because my quads and subwoofers did create a 8 or 10 dB bump which I cured very adequately with the use of a Rives Parc equalizer. Like magic. So I did use subs with my quads and totally agree they can be well integrated with esl-63s if you have the right subs and the right crossovers... in my case I used Vandersteen 2wq subs with the MH-5 ( I always get the model number a little wrong but it's the ones used in Vandersteen 5 system). Really amazing.

 I swore off solid state amps (it would be fun to ABX someday and see if solid state could fool me) though, I, I I am a believer that, in general, it is about execution and not about materials or topolology!)... But I had a great experience with subs and esl-63s because I lucked out and found subs that are fast and have pretty brilliant xover approach.
Someday I may go back to quads... They do things few speakers do in the treble region,  in my view. Peter Walker was a genius, and Peter Snell too. I should lobby to have my first grandson named Peter.

Did your listening test with Peter include tube amps, or was that the time period when tube amps were out of Vogue?

I have used 6336 single ened amp to drive stacked quad57 to my best satisfction.  Stay away from low damp factor tubep such as otl amps. Do not use sub woofer  unless you are not capable of detect  any phase shift of the speakers.