audio question..

The HDMI from the Xbox will carry both audio and video to the TV. You can buy a dongle box for the X360 to allow you to use the optical output to your receiver and run your HDMI for the video.

It should, quite a few people find that when using HDMI to the reciver they have problems with sound. Try andf check on your reciver if there any lights/menus/displays that let you know your still getting a DD 5.1 signal and not PCM 2.0 signal.

I've resorted to HDMI for picture and Optical found sound as it always works.

If you're having audio issues with HDMI, go to your sound options on the dash, set to 2-channel, then set back to 5.1. That usually will fix any of the common handshake issues with the 360.

It varies from game to game - many games don't utilize the center channel.

i thought a developer requirement for the 360 was DD5.1?

Every game i've played on the 360 so far has DD5.1, i've yet to see a game without it.

The 360 encodes core game audio into a Dolby Digital 5.1 stream by design. A developer can optimize their game audio code for 5.1 streaming in the Xaudio API during development of a title but there is no actual Dolby Digital work in a game except for the occasional cutscene or video clip that has a pre-encoded track. The only requirement is that the game be compatible with the DICE (Dolby Interactive Content Encoding) technology built into the console.