How does solo piano help you evaluate audio gear?

The most important thing about piano is already said here:

So what does piano reveals exceptionally well to my ears?

- musical scale, unlike any other instruments offering an incredible, unparalleled range.

- higher and lower scale in frequency range than any other instrument.

- both treble and bass clef while most other instruments reveals only one or the other.

But i used the human voice first before piano.... Chorus or single voice... Because evolution trained us one million year to recognize a voice anywhere in any location at the risk of death...

After that i use piano also....

Third i used brass and violins...

but never mind the instruments, each playing note must be SEEN to be  a dynamical flowing volume in the room with a micro-structure like a skin with his own texture...

«Sound smell»-anonymus acoustician

Really important for detecting crossover anomalies, dynamics, and tone.

@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.