This is a very tough question! When I go out to do serious seat-time with equipment, I usually bring a list of several songs or pieces of music but virtually never listen to the entire piece(s). I generally listen to a minute or two of various parts of those songs or pieces, parts that have the most challenging or revealing frequency ranges. For example: I usually bring only music that I am very familiar with and, preferably, music I've heard in live performances. I will bring examples of male and female vocals, piano, heavy bass (e.g. drums; pipe organ; etc.), mid-range rich stuff (e.g. Jazz), acoustic stringed instruments (e.g. guitar; stand-up bass; harp; etc.), exotic instruments (e.g. think Hiroshima), high-pitched instruments (e.g. Triangle) and just a bunch of different things. I find that various components, especially speakers, have a difficult time realistically reproducing brushes on cymbals and drums. So, I will bring some of this. I find instruments like Tuba and synthesizers are also challenging (e.g. Moog Synthesizer). One recording I like to use that covers some of this is a good recording of "Tubular Bells" by Mike Oldfield.
