How does solo piano help you evaluate audio gear?

I also listen to the hammer strike, the initial overtones, and their decay. Instructive in terms of how the system handles the whole sonic envelope, not just wide frequency range. I’ve had a couple very good pianos, including a vintage Bosendorfer. You can make easy comparisons by ear with the live instrument and a recording. (Every piano, even the same brand/model, tends to sound different. Someone who restores these instruments knows how to voice them to achieve different tone and attack).

The trick is finding good recordings. Either the piano is too closely mic’d or is presented in miniature compared to a full sized grand.

@serjio 've had my pianos voiced at some expenditure of time (and some money). They sounded fabulous for the moment, and maybe two weeks out before souring. Bernstein's guy told me to get rid of the old Bosendorfer and buy a Steinway. 

You are right about EQ. It is frowned upon in high end circles, even the top end stuff (eg. Cello) is regarded as a curiosity, not a "solution." 

I'm not sure I fully understood your discussion of manufacturer offered configuration variables, I think there are simply too many variables for a single manufacture to  be responsible for some non-existent standard. 

But @Frogman- you have an advantage in that you know the range and color of the full orchestra at "full frequency bandwidth" for real, so you don’t need easy cues to assess home reproduction. You are also exposed to the real thing more than most people, I would guess.

The most convincing piano recording I have is on an obscure label, Leo, and contains a blues/piano/voice thing. The piano sound is deranged. The rest is a matter of taste. This.

I use piano as a reference because I know the instrument, but think the variations among individual instruments, as well as how the recording is made, may be variables that are obstacles to the piano sounding "real enough." I needed more gravitas in the bass including upper bass, and got it through a change of cartridge.

The system is not perfect, each of our ways of judging things is dependent on a host of factors that go beyond sophistication in the hi-fi marketplace.

You mentioned decay. That ambient space, if well captured through mic set up and acoustics, is what I’m about. I know what a real piano sounds like (recognizing the variables). I am now able to hear bass with dimension in space, as well as some pretty convincing "down low" sounds which do not lack for volume.

How real compared to a recording is an almost impossible subject. If the recording captures the energy of the performance, I’m often happy.