So, this thread has degenerated into the total non-believers of any difference and those who DO wonder what we are not measuring or interpreting because we do hear differences. So much for trying to move forward in measurements. If I can hear a difference, it is measurable. SNAID is a great wheat from chaff first pass as products that measure terrible in that regard usually sound terrible. The question is in the top half. Decent measuring to superb. They don't exactly track.
I would suspect, there is a threshold of parameters we are not testing or interpreting that beyond no one can hear a difference. That would be the holy grail line in the sand. It would also probably put a lot of EGO brands out of business. From a Benchmark up to kazillion-dollar monoblocs sitting on platinum spikes, is there a difference? I am not sure. I can't afford the Benchmark, so I am not there yet.
I do know when I listened to several well made mid range integrated amps ( Atoll, SIM) they sounded the same to me. When I heard an Arcam and a Rotel, in a bad big box room, they were night and day, Even crank the Rotel clearly louder and it still was lifeless. Typical "no power supply" defective sound. I suspect, the Arcam would have been indistinguishable from the SIM and Atoll as they were all "good enough". This is why I believe we need some sort of burst mode testing on amps. Not a simple transient. Something that shows the effect of the rails collapsing, or is it poor PSRR? Is it different amps handling the reactive load differently? They do. Is where the feedback point physically wired allowing load dependent parasitic influence? How well things like this addressed are not always cost driven, but designer skill. I have built amplifiers and played with these things.
Some of this non-belief can easily be differences in hearing. I have been very careful to protect my hearing. That is not true of most people. I would like to see any participants in an ABX have a hearing test , results held for analysis not to bias their perception. I know for me, because I focus on it, I do not hear the "problems" as clearly as I did 30 years ago. I know as when doing impedance sweeps on tweeters, I know where I hear them fall off and noticed it is lower than it was. 40 years of speaker building, I have measured a few tweeters. I can still hear these issues. My wife more so.
Maybe, try this idea. We did not have children, so we did not deal with several years of our genetic evolution sensitivity to that 3K band. Maybe parents have adjusted to tune that out, where we have not. So we may be more sensitive to smaller imperfections in the sensitive band than parents. I know a weekend at my Nephew's with three young ladies ( 4,5, and 6) and a 2 year old, my hearing and nerves were shot.
I observed in college, engineers had expensive stereos, music majors cheap ones but a speed control on their record player. Almost uniformly. I can't tell if a 440 is 445, but a music major can. A difference in subjective hearing.
So, can we look to the science? What can/should we measure?