so what your asking is can you play cod vent etc on your computer throught your headset, and on the same computer have audio out to speakers for music etc?
get cod/vent etc to output to the port your siberias are plugged into, cod requires it to be the default device; then make your media player output to whatever your speakers are plugged into, not hard.
just bumping, did anyone ever figure it out, atm i have like 800 songs on my ipod coming through speakers, id rather be able to use itunes, and youtube etc for speakers too.