There is one music track for each chapter, and there isn't any way to change the music other than muting it and playing something in the background from your own library using a music player of your own choice.

To be totally and entirely honest this was all we could afford. Although you must bear in mind the game was initially designed for mobile devices and intended play session time was about 5-10 minutes so the repetitiveness of music wasn't an issue. But we understand that listening to the same 30-second loop can have... some negative effects on one's sanity, even if the music itself isn't bad.
However right now we're focused on making sure the Steam Cards and all the rewards for completing the set are of highest quality possible, and next we'd want to tackle the problem of implementing at least some of the Steamworks functionalities. That doesn't mean we definitely won't improve the music to be more suitable for longer play sessions, just not in the nearest future. (There is also an issue of finding the right composer who would capture the game's feel, but that's a completely different topic.)

Try playing some Touhou music on Steam overlay. Especially songs about Flandre and Remilia. They fit into this game perfectly as they are vampire characters just like Mina.

Here I'll link to you some songs you would probably like:
http://www.youtube.com/watch?v=VIop055eJhU
http://www.youtube.com/watch?v=vAlEtcGOe2I