Recently in my audio programming class, we've starting working with a library called FMOD, it's really wonderful! It's fast, easy and portable!
I'm pretty sure it supports all of what GE supports and more! This would most likely fix the music/audio problem with Linux as well!
http://www.fmod.org/
Makslane, akr or sky, please check it out You even have custom dsp effects and everything! The only thing you need to include with your game is a dll, FMod can do both hardware and software mixing flawlessly!
I suppose GE would use FMod ex programmer's API, Fmod designer also provide a really easy to way to implement sounds that don't sound simple
I could try adding it into GE myself, but I rather wait until I get a little more programming under my belt, I feel like I wouldn't be able to understand how GE works just yet But if you have questions about it, please ask! I can always ask my teacher if there are things I cannot answer
Oh, I think I forgot to mention... It's completely free!!