I just started setting up my home theater, and one issue that i had is that the receiver I bought only had 1 optical and 1 coax ports for digital sound. The optical was taken up by my HTPC and I wanted to use the coax for something other than my subpar DVD player (old Aiwa model). I also have an Xbox w/ the HD AV connectors (Component and Optical/RCA sound).
This hack is essentially an Optical to Coax conversion for the HD AV cable. I uploaded a rough image to help you with it (it's VERY easy, and only took me a few minutes to figure out). BTW: thanks to Matt Staroscik for the inspiration.
I am not responsible for damaged/broken/messed up equipment - this worked for me, however.
Tools needed: Soldering Iron, Solder, screwdriver (to pry open the connector), wire stripper and cutter (to strip the RCA and also to cut the head of the RCA when needed)
Anyway, here it goes:
Step 1) get a single-connector RCA cable (stock is fine, or if you're fancy, use a monster. The only thing is that you may not be able to fit a monster into the connector.
Step 2) cut off the head of the connector and there you will find two sets of wires (#1 in diagram). In mine, one wire (red) was in the middle (a), surrounded by loose wire (b). The red is the "hot" lead in the RCA wire, the black is ground - simple enough.
Step 3) Get your HD AV connector (#2 in diagram), and open it up. You will not be able to put it back together as you had it before, because Microsoft decided to make this shell un-resealable. It's ok - I used take to patch it up! Anyway, when you remove the shell, you will see a very closed metal connector, on top of which, like a burial mound, you will find your Optical connector. Luckily, we're not looking for the actual connector, rather, for the other side of its PCB.
Step 4) Get your iron ready, and when its hot, apply heat to the solder on the sides of the connector to unsolder it from the inner shell (where the optical connector is). When you're done, you will be able to remove the casing and see the actual connector, dangling on a wire.
Step 5) When you see the actual connector, bend back the optical adapter to see what I illustrated in #3 - a PCB with three wires connected - a black (ground), red and white. For our purposes, the optical connection only uses the white and the black, with the red used for Stereo (we don't need no stinking stereo, we need Dolby Digital).
Step 6) Solder the red lead from the rca to the white connection on the PCB (you don't need to put it RIGHT on the white, but make sure that it's on the same lead. Do the same with the loose wires and the black.
Step 7) When you're done with this, make sure you isolate all of the wires with electrical tape (you don't want shorts and such inconveniences).
Step 8) Put everything back, attach the metal shell to the connector, put the plastic back, tape it up.
Step 9) Connect to your XBox, connect the Coax to your receiver and enjoy #4 - DOLBY DIGITAL!!!!