Sheffield Labs Drum Record
but nobody seems to recall this reference from over 40 years ago
I use original german polydoor classics box set Richter -- Well Tempered Clavier http://https//www.amazon.com/Bach-Well-Tempered-Clavier-Sviatoslav-Richter/dp/B000026OHN
Nothing challenges system as piano.
The reason I don't use Chesky label is because its only good for sound testing while I need to listen to music even when I test sound. Chesky for me -- bunch of boring audiophile toons.
I can't find much of an interest for piano and vocal together. Some of the recordings of Gale Moran(Weather Report) and Chick Corea are great listening material, but I guess not too much you can sound test on those as they're not really challenging to system due to being compressed.
The CD I've mentioned will test the hell out of system in all possible ways with sufficient intensity throughout whole piano keyboard. Playing Bach piano sonatas requires even more challenge so HUGE credit to Richter who I value and admire as well as German releases on Polydor Classics digital disks (including digitally mastered vinyl).