In the stores, I usually fill up a wallet with my most favorite CDs and test them with several. I haven't shopped for stereo stuff in some time, but if I was going tomorrow, I'd take:
Tool: Lateralus (Wide range of sound types)
Tool: Ænema (if this doesnt sound good, I don't want the system)
DMB: Listener Supported (live music)
Braveheart Soundtrack (classical type music, also movie soundtracks if I'd hook it up to DVD)
I'd burn a CD with some mp3's just to test CDR capiblity and to cover some song types I dont have on CD (VAC, Funker Vogt, etc)