I knew this thread would get to the core of perception. There's still plenty of electronics posts, which is something!
But I didn't think it would get to folks saying "well I can hear up to xxxkhz!" It seems people assume that human hearing cuts off at a certain frequency, it of course doesn't, its just attenuated, like any other filter. You can sense 20kHz if its loud enough regardless of age, you can even sense 40kHz, again if its loud enough, but as to whether one would consider that "hearing"? that is a different matter, after all we can sense 15Hz, but is it the ears sensing the stimulus?. Also, being able to hear >20kHz doesn't seem to offer any advantage, and in fact must be quite irritating (like having perfect pitch).
Some people should also let go of the idea that their senses are consistent. It doesn't matter how 'good' or clever, you think you are, or even being aware of ones own biases (which apparently makes us *less* accurate) you cannot escape this. As paulca alluded to, our minds do a hell of a lot of filtering to the raw signals our senses pick up, even to the point of pretty much creating 'experience' itself, using the real world stimulus as a guide to update its model. This means there are several layers between what sound enters your ears, and what you 'hear', and its mostly dynamic. It's the reason behind optical and auditory illusions, it adjusts 'EQ' which is why we become accustomed to the sound of certain headphones, or sound systems (including the speakers and the comb filter effect of the room).
But referring to the topic.. I think we can all agree that the "sound" of an amplifier is just one of many many parameters that affect the sound we hear. Even if we (try to) exclude cognitive bias, given the same speakers but a different room, will sound different. Also.. it will sound different depending on what you have heard during the course of the day, loud bass-heavy noise will make you less sensitive to bass frequencies, likewise with higher frequencies - the mind naturally tries to flatten your "EQ" as constant stimulus isn't novel and so, filtered out. The effect isn't particularly dramatic, but its definitely there, and not considered cognitive bias, perhaps its what"listening fatigue" is?
All this means doing A/B tests, even double blind controlled studies can only go so far. It can highlight certain limits (perception of THD, max frequency, min frequency etc..) but these should not be considered overly accurate, so any conclusions drawn should be taken with a pinch of salt. Just because a study is 'double blind, placebo controlled' doesn't make it absolutely accurate, just that compared to other methods, it is the most accurate way to access things.