From what I understand, one reason why volume control of the tracks isn't there is because of the outdated Direct X5 controls the game was built on (or something). How about (though tedious), giving the user the ability to play, stop, and adjust the volume via configured keys. In my head, I already know where some of these volume keys are supposed to go, and I have a feeling the program knows what tracks to play where and when, just not always where to start. Take for instance the Neibilheim scene. After Seph walks off, version 2 of the track is supposed to play but it doesn't. I have a feeling that it's already cued up, but there's just no way to press play.
Don't know if the guy who makes this awesome plugin is still working on this, but that might be a great solution until he can find a way to emulate or read the volume controls ingame.