Agree on classical. However, if you actually attend a concert, it’s not really that loud. Depends on the piece, but blasting some crescendos isn’t going to tell you much. I’d go for organ. It’s actually the first hi-fi rig. It’s listening to how it reproduces ranges of textures, tones, transitions from midrange to bass. And the same recording on two different organs should be radically different because of reproducing the space.
Also, play something groovy. If you move, tap toes, etc. that’s the point. If you hear a band live that just isn’t getting you to move something is holding it back. Amplification probably is a bigger source for this but lack of decent bass too. Or some call it PRAT. Things out of time are easy to tell. They just don’t swing.