It seems to me that the huge difference between a really good system and the run of the mill, is its ability to maintain the sound of, and separation between, instruments, unaffected by volume or signal. Second is the ability to produce extended bass that is not just a home-theatre style rumble.
As such, I don't think that jazz or Pink Floyd is going to amaze anyone as much as some big orchestral stuff with its huge dynamic range and broad stereo image with individual instruments spread across it (not just pan-potted). So first I would play a track something like this:
http://open.spotify.com/track/0F0nvduoPIDIplzkGY3Rfw
(Korngold: Between Two Worlds:The World at War/The Next World/The Blitz in London/The Ship from An Introduction to Entarte Musik)
If your system can reproduce a live-sounding rock track in your living room at realistic levels, that's going to impress anyone. Such as this excellent track by Neil Young and Crazy horse (that even sounds great in 16/44.1 kHz
):
http://open.spotify.com/track/72DgEGVM9ezqKOB0Kxo2wV
(Neil Young and Crazy Horse: Carmichael from Greendale)
Synthetic sounds can go beyond 'natural' and make good demos of a system. Here's an amazing track that combines overpoweringly-deep bass and ear-tickling stereo analogue synth sounds:
http://open.spotify.com/track/1Pz0pTjKwlM52IdWZU4s2K
(Goldfrapp: Crystalline Green from Black Cherry)
My nod to jazz would be something like this which has got quite a hard dynamic edge tempered with rich, resonant bass and features just a few instruments recorded cleanly with space between them:
http://open.spotify.com/track/17uPeGmP6DrxfIRcNy9067
(Bad Plus: 1979 Semi-Finalist from Give)
Finally a crowd-pleaser that sounds fantastic on a larger system particularly because of the deep bass, open space and virtuoso production:
http://open.spotify.com/track/4veRrJjAXnJi95hlJvQUzc
(Grace Jones: Slave to the Rhythm from Tracks in Private Life - The Compass Years)