Now you are talking in language that I can understand.

The fact is, most popular mid range amps are not going to have trouble in terms of "superior" channel separation (some are dual monos anyway). To say one images better and throws a better sound stage due to it's "superior" channel separation, is like saying one amp sounds better due to it's "superior" FR that extends to 50,000 Hz +/- 0 dB when it is a known fact that normal human being (except new borns) cannot hear anything beyond 20,000 Hz and a good % of the population wouldn't even know the difference if you filtered out anything above 15 kHz.
I do believe that in many cases it is mainly Placebo at work. More and more now I simply focus on enjoying the music itself and try not to think too much about those superior specs that may be missing from my system.