Hoping someone might be able to lend a hand here - I am using an original 360 elite (not S), and have it connected via HDMI to my television and via a slim AV adapter with optical output to my receiver for audio. Unfortunately, I am not getting any audio output from the 360 to my receiver via the optical output. This was working at one point, because I had it hooked up this way right after we purchased the 360. For the past couple of months, the system was set up in a different location and did not require the optical for audio, so was being used strictly HDMI. Now that i have it hooked back up this way, it seems like the system just is not sending audio signal across the optical output.
I know the optical cable itself is good because I've been using it with a PS3, attached to the same receiver, so I know the optical port on the receiver is good also. I have no reason to believe anything is wrong with the AV adapter for the 360 because it has just been sitting unused.