neutrality vs. realism

Phew...I thought they were the same thing!
OK, inasmuch as "perfect measurements" don't sufficiently exist to guarantee full "neutrality" (or realism, by my acceptance), then good science doesn't necessarily provide sufficient realism. Granted. But since when does neutrality not equal realism? By striking a difference between the words we continue to muddy up these psychoacoustic waters.
Amps do things that aren't yet measurable that make them more "musical", which is assumed to be approaching purer neutrality to the upstream source. Otherwise a preferred "musicality" that's NOT neutral is simply a euphonic distortion (tube's 2nd order, for example), or coloration (HF droop, e.g.). Let's not confuse photography with painting.
Those who say that spectral neutrality is a prerequisite for a "musical" presentation also miss the boat, in that one can have the latter without flat frequency response, for example. Can we not just say that what we like may not be the objective "truth" electronically all the time, and be done with it?
Sure it seems that the very best systems are as neutral as possible, by definition, but there are as-yet unmeasurable criteria that are ALSO optimized that then lead such systems to be described as musical, as well, to out ear/brains. I need more coffee....Ern

Your mind is pretty well made up that "ultra high-end" amplifiers sound so much better, why bother ask for opinions? Again your post here seems to be pretty much a closed loop. Contrast your post with that of the fellow who bought an Onkyo receiver at a yard sale and is pleasantly surprised at how good it sounds. Listen to what you like and don't fret too much over these questions. If you feel that some distortion, some noise, some non-linearities add to the listening experience, consider yourself part of the new breed of audiophiles who have helped sound reproduction complete the circle. Good day.

This should be a good discussion. First, consider the older amplifiers with 0.001% distortion. Lots of feedback to give great specs, and terrible sound. I think we have come to realize that specifications do not equal great sound, but your question I think really goes to the heart of the listener, more so than the equipment. Even though you stated this is not tube vs solid stat I think it is a great example: quality tube amp, vs a solid state amp in the same league (price, quality etc). The solid state will "measure" better in almost every circustance, but some people will prefer the sound of the tubes. Analog and digital playback have the same phenomenon. In almost every aspect of measuring the CD will win, but many, including myself, prefer vinyl.
Now, because I am an acoustical engineer and design listening rooms for living, I would like to take a small twist on your topic to an area I know a bit better--the room. The room has, I think more variation, and in many cases more impact on the listening experience than any individual component. A room can actually be tuned to an individual's taste and there are always give and take. Let's start with the extreme, a studio control room. This is very neutral, and usually sounds a bit on the dead sound. While not over damped, it is damped more heavily than most rooms to keep reverberation times to a minimum. It is usually engineered the Helmhotz resonators and has an absolute (or close) frequency response. In most cases (with smaller studios), the heaviest damping is behind the speakers, and if there is a live end, it is behind the engineer. This is because (as an example), the live end is usually where the performers are and the dead end is behind the microphones. The goal in the studio is to give back the sound to the engineer as though he were standing in the performers position and the mics were speakers. This works great for the studio engineer, it would not be so great for most listeners. We have designed rooms with longer reverberation times for some people than others. Some want an overdamped room and a very dry sound. Some people play at high volumes and need sound isolation as well as slightly more high frequency attenuation.
Now to take it one last step further. I think you've really gotten to what building a system is about. It has to be musically engaging. There has to be the magic--not just the notes. Someone may be able to play the notes of a song, but they can't play the music. They just don't seem to have the sense, pacing, and naturalness to really play the music. I've heard many concerts that I felt like that was the case--and then I've heard others that I was just in awe of. In building a system, I think it's the same. While every component may not have that etherial magic to it, when combined with other parts of the system it does create a real naturalness, and a large part of that is the speakers coupling to the room. The most distortion, phase and otherwise, occurs due to this interaction. This interaction is need to give you a sense of space and dimensionality, which to me is what creates that naturalness in the presentation. Have you ever listened to a pair of speakers out in a pasture--no walls no interaction. Probably wouldn't sound too good--but you would have gotten rid of the one thing that causes the most distortion--the room.
I think I've said enough. I'm looking forward to others thoughts on this one as well.