Listening too hard
> I think I can detect an instantly perceptible MP3-FLAC difference
Maybe you can - but does it really matter?
Most people I know listen to music as a form of entertainment, generally as relaxation. They don't listen to it on the assumption that they will be tested on it's content and clarity after hearing it. Likewise, they don't listen, eagle-eared. waiting for that instance in the third passage where the conductor's tummy rumbles - or where you can hear the tube train rolling past the recording studio.
Having said that, the first time I plugged in my home-made transmission line speakers (still with me 30+ years later) and cranked up Wish You Were Here it was a bloody revelation. I have witnessed similar reactions when I have plugged in a basic 2+1 speaker system into friends' flat-panel tellies: where did all that sound come from? after listening to tinny audio for an age and not realising there was anything better.
Although those step-changes are huge. Whereas the difference between an average quality MP3 and a FLAC is perceptable - but you're merely detecting the difference, not listening to it. And as soon as someone in the upstairs flat farts, or a car rumbles past, the difference vanishes. As it also does on anything less than my TLs.