Hm. Coming to think of it, I don't think I've heard any more than three (four, tops) different tracks to each of the battle phases, even though I have about 8 tracks listed for use in each phase. Might be 3/4 is the magic limit?
But then, of course, how does the process choose which tracks to play, out of the list given? The tracks it does play during my battles are placed rather randomly on my lists, so I can't say that it starts at the top of the list or anything like that.

Also, after I added my new tracks, I've lost the little piece of music that used to play in the background when the "You've Won/Lost the Battle" window popped up after battle. Kinda strange, as I didn't make any changes to that music when I added my own. You've encountered anything like that?
Still, it's a small price to pay though, for being able to make a cavalry charge to the sound of "Anvil of Crom"