I have just downloaded MM7 and started it up. The music comes in very loud straight away and when I go to the settings and move the slider down, it makes no difference at all.
I can't have that loud music on while I play, but I'd rather not have to switch off all sounds.
Have you tried turning down the volume in your Windows sound mixer settings? I think you can turn down the volume for the game itself once you have the sound mixer and the game open.