Trained ears.

If you can tune a piano, then you know what the notes should sound like.

Just listen to as many systems as you can, and form your own opinion.
B

gawdbless,

You hear pitch with exquisite precision because you understand the concept of pitch extremely well. Okay. So what's your understanding of grain? Attack? Decay? Ambience? Sibilance? Harmonics? Timbre? Timing? Presence? Palpability? 

I'm no piano tuner, but pretty sure you could write volumes on pitch, tension, humidity, fundamental, harmonics, etc. Some of what you're familiar with you will be familiar with here. A lot of it will be new. Doubt you've spent much time listening for grain. No piano ever made was grainy. Grain is an artifact of the recording-playback chain. Just one random example.

I was once like you, in that having played musical instruments I was pretty good at pitch and tone. Yet I couldn't tell one CD player or amp from another to save my life. Now, no problem. Takes a while, but you can learn.

If you really do want to learn here's the best help I know of:
https://www.amazon.com/Complete-Guide-High-End-Audio/dp/0978649311

Robert Harley clearly covers not only all the equipment, but how it works and how to evaluate it including how to listen. Whole chapter devoted to how to listen and why and what to listen for. All the terms. Been out forever but updated and so well done that even my 30 year old copy is still worth reading.

There is the classic book by Alton Everest called Listening Skills for Audio Professionals.

More recently, Jason Corey has written an excellent book which is complemented with online training by the author.

And before you ask, Yes I am trained. And Yes, training makes a night and day difference. Critical Listening requires training. Those who listen to music daily are like frequent flyers. They have been to many places. Can they land a commercial jet at SF airport - Absolutely Not - they are just armchair amateurs.

Thanks for all the great advice chaps!. I did borrow a reel to reel tape deck with my bands music that we recorded in a studio as well as recording my own piano at home, a longgggggg time ago. The sound through my Impulse H1's Horn speakers was really good at getting all the nuances of the band and especially my own home piano at the time with all its quirks which I recorded. I should have recorded just  the 4ths and 5ths or major 3rds and 6ths on the piano and then played it back to see if I could hear the 'beats' of two notes not in unison with each other, as the only pure notes are each note itself if there is obviously 2 or more strings to each note or octaves, everything else is tuned 'off'. That would have been a good test for the loudspeaker, or any speaker!
I can record my piano, drum kit and synth with my Yamaha AW4416 mixing desk, I only need to buy some microphones. I would be pushing my luck by buying a reel to reel at present, lol.  Thinking about my buddy who is in Germany now probably still has the reel to reel tapes of the band.Hmmm.....
I think I know 'The Wall' by Floyd the best probably musically and when the vinyl album was played with my H1's, with an LP12 TT and a pair of tube Audio Innovation 1000 mono block power amps and Audio Innovation pre amp, was a totally awesome sound to my ears.