Glad to be of some service. The last resort, that will definitively prove that it's a sound issue - is to use the /nosound switch on the command line that launches Supreme Commander. This will turn off ALL sound - and if the game is stable then, you have proof positive that it's a sound related thing.
Some people have had success in these matters, just getting rid of the music files - which is just a matter of deleting the files associated with the game music - but I'll leave that for another discussion.