The music was made in Bosca Ceoil, which I hadn't used in a very long time so i cant remember if there was a volume control option.
I hadn't written much music before this, and I think it shows in the boss theme especially since it was the first one I did for the game, I'm not entirely happy with that one and I can tell what you mean with the micro-tonal chords. Very sorry about that, but I'm glad it didn't stop you from having a good time with the game!
I'll see if I can fix the volume issue in a future update (and maybe try recreating the music because I forgot to save the files)