I think it’s really important to not ruin your favorite music by turning it into test tones! (Been there, done that!)
I try to use a variety of material, but always wish i had access to recordings of live, acoustic instruments, that were made when I was present at the actual performance–seems like that’s the only way to tell whether your gear (along with the recording equipment) is telling the truth or not.
If it’s more about My-Fi, than HI-Fi, than any recording will work, as long as you have a preconception about how you would like it to sound. Like, if everyone is wearing only white clothing, and you are trying on tinted sunglasses…
I try to just enjoy the music, and check in on how I am reacting to the playback - and how much time has dissapeared. I bought some iems recently, and let them burn-in for a few hours during work, then stuck them in my ears at about 6:02 PM (I work til 6). Realized that it was 11:30 PM, and that I should hit the bed, when i finally pulled them out of my ears-- that’s what I mean!
I think it was a Cassandra Wilson album I was listening to when I realzed how late it was. There was no bass, mids, treble and soundstage - there was only CVassandra singing to me, and the musicians playing her accompaniment. yum