How does solo piano help you evaluate audio gear?

@brownsfan @lalitk and others -- this is great! Thanks so much. I really do find it helpful in addition (of course) to the human voice. There's no either/or in any of this.

What is hard with pianos is that not having heard the piano in the recording there is a huge "guess factor" as to whether component/speaker A or B is getting "closer" to the original. One thing I heard today, though, which is not compromised by that problem was a piano with high notes that sounded like a toy piano. That clearly is a speaker not dealing well with tonality/overtones.

@hilde45, I use the ECM Schiff Beethoven recordings.  They are good recordings. Schiff used a Bosendorfer for some and a Steinway for others.  I think I can tell which piano he used on my system.  I took one of those recordings to an audition, and the speaker failed miserably to get the tonality right, though it sounded pretty good on orchestral works.  None of us were in the mixing room for a recording, so it is always a guess.  Assuming the recording engineer knew what he was doing, we make a judgement on what sounds "right."  

Agree on massed strings being an ultimate hifi litmus test.

You cannot have a piano right and violin wrong AT THE END...

You cannot have all these two right and voice wrong AT THE END of the process...

First voice... Because we are inwardly tuned to recognize voices...

Then piano...Because of the huge dynamical field covered by this instrument...

Then violins and brass and wood...Or orchestra... Because the great number of this different timbre playing together distinctly is great test to end...

There is an order for me because i use that to test my room for the tuning for months...

IMO, the problem with using a piano as a reference (generally) is that there are so many poorly recorded piano pieces. The piano must/has to be the hardest instrument to get recorded correctly to fully reproduce its the broad and nuanced (detail) sound capabilities, much more apparent live.