Its a known fact that the human brain cannot remember differences in
sound sublties for very long at all, so again your brains predjudices
often come into play to color the sound in a way you dont even realize
(but maybe not in this case) ...

The brain ALWAYS "colors" the sound. That's its job. Contrary to popular
belief, the human brain is NOT a sound detector. It's not interested in
revealing everything about the sound. Instead, the human brain's job is to
FILTER the external stimulus and provide the information in a simple manner
so that the brain's limited processing capabilities will allow the human to
extract the information deemed important and process it in a manner
consistent with human function. As such, even though the mechanical
transduction process in the ear contains most of the information that the
loudspeaker provides, the neural representation of the sound is filtered
even at the earliest stages of auditory processing. By the time the neural
signal even reaches the brain, a considerable portion of the sound
information has already been filtered out. This, along with more central
levels of processing, is the basis for finite psychophysical thresholds.
This is why we cannot perceive every aspect of the sound presented to us.
And as you astutely point out in the remainder of your post, being able to
provide real-world measures of quality is dramatically colored by the fact
that we're not oscilloscopes. We're humans.

IF and IF is a HUGE word here, one amp is compared to another amp
at EXACTLY the same amplitude at EXACTLY the same frequencies
with both amps playing EXACTLY the same then of course there
will be absolutely no way to tell the difference even in a good A/B
test.....

You say "of course" here, but many people, including Howdy and Pug do not
agree with this notion.