Goros - Please stop trying to help in this thread. You are only doing a pretty good job of lying to this poor man.
jkspinks - Do yourself a huge favor and ignore Goros.
Your receiver does audio over HDMI. This means you can use any HDMI cable (monoprice.com!), and get audio+video to your receiver. Then the receiver will pass the video out to your display. The audio quality compared between the 360's HDMI connection and optical is exactly the same. It is the same DD5.1 bitstream coming out of the Xbox, either way.
Yes, HDMI is capable of different audio types than optical/coax supports, but none of those are used on the 360.