For the record we went with shine on you crazy diamond from wish you were here with the quiet opening and punch when the rest of the band kicks in. Sounded great.
If I want to test it out it might be something like Tipper.
But, in reality, it would probably be something from my favourite album pile like NIN, Squarepusher, Allman Brothers, Four Tet, Caribou or something from the 90s.
Probably either something off the Dune soundtrack, Interstellar soundtrack, or Krigsgaldr from Heilung's Lifa live album. I might be a bit odd with my musical tastes
I usually play Enigma's first album, because I use it as reference recording to get everything set up. Either that of "Cherish The Day" by Sade. After that, maybe something by Om. https://www.youtube.com/watch?v=kKqoNrZ00Bg
I like flac as it's versatile and I can transcode it without fear but it would surely take an actual mutant with a few million in stereo equipment to tell the difference between flac and a decent lossy rip.
If you mean dialing in the sound and using songs to test the system, either Hooked on a Feeling, (listen for the bongo man), ain't no sunshine, or Bad.