Re piano. I rediscovered an album from long ago that I found in the cut-out bin of a long-forgotten record store. The title is "audio symphony", Check up your sounds Vol, 1. It was produced by RCA Japan in 1976 and distributed by Audio Technica.
It has a 14 page insert describing all the equipment used and even includes the music score sheets. Although it goes into minute detail of the equipment used it does not describe the piano. Notable is the use of an Ampex 440c and Studer A-80MK II reel to reel. Both running at 30 ips.
The sound quality is astoundingly good with dynamic range and quit background even on my modest system, The bass quality of the piano is remarkably good but I would agree that it is not the best test of a systems bass agility and depth.
Also, as someone else mentioned bowed string bass (in this case a trio playing in unison) is also a pretty good measure,