if you play COD2 here is a test you can try, i did it last night while thinking of this thread.
Go into the training at the very beginning of the game, when your commander is giving you orders look directly at him, the sound should be coming out very clearly from your center channel. Then turn your back to him and the sound should switch to the rears. Then do full 360 spins and you should hear the sound pan across all of your speakers. Then look directly at him again and it should focus the sound back on the center channel.
If this does not work there is a problem somewhere in your wiring, electronics or Xbox360. At which time you will have alot of trial and error to do. I hope this helps.
I just did this last night so you should get the same results that I did.
