Now to be controversial, not normally something I like to do!
By and large that is correct with the amps, strange as it may seem, humans aren't the mystical beings the pushers of expense audio tat like to make out we are! I am particularly scathing about the drivel put out by cable manufacturers and their ilk, there is no physics that lies behind what they claim. Audio homeopathy. If people want to buy it that is fair enough, it does no harm to anything but their bank balance.
We are good at discerning some transient distortion, clipping, but not very good at some harmonic distortion, and quite a lot of people can identify hard filtering, so 'brick wall' filtering. Which is why we use higher than Nyquist sampling rates, its not to give more high frequencies, its to ease the response of the low pass filter. Most people hear things which are actually down to frequency response differences (usually the amplifier (even pre-amp) hasn't enough drive) and poor contact in connectors. There are some super-listeners/hearers which can hear way more than the average person, but they are as rare as rocking horse sh*t, but they do exist. I can listen to mp3 in the car but not on my home system, it doesn't sound as good, but there is a measurable reason why.
As an electronic engineer if I can't measure it I can't improve or correct it. Peter Walker the founder of the Quad amplifier company was a very good engineer and realist, and designed some great and importantly, reliable amps. I often listen to a mix of Blu-rays, DVD (-A, DD, DTS), CD, and vinyl, the distortion 'differences' are quite large between the different sources but its actually a lot harder to distinguish between them than you'd think, and after a short while you're listening to the music (which is the purpose after all!) and don't notice the source.
Many moons ago: For quite a while until I could afford a 'better' amp I had an Amstrad amplifier (not great specs, which I bought in my 1st year at Uni) which cost £30, driving my AR93s which cost me £300 (a months post tax salary then!). A friend came round with his £400 Cambridge Audio amp and says you'll hear the difference, lower distortion, better all round - it improved the Bass response a lot as the Amstrad really couldn't drive the speakers that well, no discernible difference in distortion, my friend couldn't understand it!
