Ah, fudge. :( So we have a questionable playback infrastructure combined with music that I've never tried before on this system.
Guess all I can do is start with the two MP3s that have played so far, see if they're consistently triggered, and then test out the rest one-by-one.
Anything known about which codecs work/don't work? Will it play WMA? RAX? M4A? (no, that's not the problem, trying just plain MP3s so far, but I noticed it will let me select other kinds of files if I show all files)