If your sound card has optical input .. you can run an optical cable from the xbox to your pc ? Just a thought .. not sure what your setup is or even if your pc is on when you are playing.
ya i can run optical to my pc... but the optical is part of the cable they give you, and you cant have that cable and an HDMI one plugged in at the same time..
...OR you could do the hack to remove the casing of the optical cable and have both HDMI and optical plugged in at the same time, without having to fork out a few hundred bucks.