Oh, also check when the PS3 is playing a CD, for the pop-up setting, and the volume control there. Make sure it is at 0, not + or - anything.
The 360 is sending a lossy DD stream with as 5.1 with 3 channels of silence. Which is really annoying because you can't apply Prologic to it because the receiver thinks there is already surround information present. I guess you could apply IIx, but that'll just take the silence of the surround channels and steer it to the rears so they'll be silent too.