I'm like Tim--I have a long set of tracks I listen to reveal differing aspects of a system. Here are some and what I listen for:
Arturo Delmoni-Songs My Mother Taught Me--naturalness, space, depth
Bela Fleck--Cosmic Hippo--Bass, bass and more bass
Brian Bromberg-Wood--natural double bass
Doc Watson & Dave Grissom-Sweet Georgia Brown--separation between folk instruments of 2 guitars & mandolin
Fry Street Quartet-separation between instruments of string quartet
George Thorogood--Movin' On Over--recorded hot, so if you can sit through it, your system is balanced well
Contate Domino--individual voices in a large chorus in a big space
Getz & Gilberto-Girl From Ipanema--close mike male vocal
Chesky Area 31--clear dynamic orchestral with multiple hand clapping in percussion section
Cantus-Let Your Voice Be Heard--Male chorus with a very delicate width balance and individual voices
Eric Whitacre-Cloudburst--large chorus, looking for width and individual male & female voices
FIM K2HD Sampler--Flamenco--guitar with 2 dancers in the back--looking for separation between the two dancers
Alison Krauss-Forget About It--If your system is a little hot in the highs, she will sound forward & a little harsh instead of beautifully sweet
Chris