I have a question: For all of those who believe no one, not just you, but no one else, can hear any difference in an amp or DAC, why are you here? Would you not have gone to Best Buy and bought whatever was cheapest with the features you want? All the same right? Or do you believe at some point, the differences get small enough that you can't hear them, so you believe no one else can?
Some of us do hear a difference. Probably not all. We do not have to prove it, and you do not have to disprove it. The question is what is different, can we measure it, and can it help to make a purchase decision? That is the only reason to be on this forum. I believe there is some point, if the tests were inclusive enough, where all would not hear a difference. I want to know what that set of parameters is. If it is different for everyone, highly likely, and you could figure out your threshold, then you have simple price shopping for above that threshold.
If you have been in a blind ABX of amplifiers, you would know many do sound identical, some differ. Of those that differ, the untrained invariably prefers those with a little more distortion. Ones with a lot do usually come up as failures. Why? How much? Can we quantify it? With a simple THD number, we are not considering preference for even or odd order, lower throughout or higher low order tapering off quicker but producing the same THD + N number. Measurable. Audible, by at least some of us. The speaker load can effect the amplifiers distortion or not by an order of magnitude. Also measurable. Is that taken into account? FWIW, the tests I sat in on were so long ago, differences in amps were a lot greater. There are quite a few today I suspect are all good enough for everyone unless there is an additional personal filter favoring one distortion over another or lack of any. Again, can we quantify it?