What's Coax Digital? Variously called SPDIF, RF and "coaxial" cables, these are plain old RCA cables, just like the ones used for analog audio. You can buy expensive cables for this purpose, but before you do, try one of the RCA cables you have lying around...
... then you undoubtedly want to hear your games in Dolby Digital! Unfortunately, your Xbox only has a Toslink-style optical jack for digital audio. Perhaps you are having a hard time finding a cheap optical cable, or worse still, maybe your home theater receiver only has coax inputs. We can't change your receiver, but we can mod your Xbox and add a coax audio jack in about 10 minutes.
Xbox 360 Support But what about my Xbox 360, you say? Never fear, this hack works for the 360 too! Matt Warnock has posted detailed instructions and photos for modifying the Xbox 360's S-Video and HDTV/composite video AV packs.
Disclaimer: If this mod fries something expensive, don't blame me. No one has written me with a horror story yet though, and this article has been online for a few years now.
What you need
1 Xbox Advanced AV Pack or HDTV AV Pack
Low-wattage soldering iron
A bit of solder
Tiny Phillips screwdriver
Optional: Female RCA connector, drill
What you do
Peel the label off the AV pack, exposing the screws.
Unscrew and open the case.
Unscrew the thing holding the PCB down and remove all the guts from the case.
Decide which of the 3 RCA jacks you can live without. I chose the right audio jack but any should work. (Or, be 1337 and add a fourth jack! See the HDTV Pack picture below for ideas.)
Snip the wire leading to the jack you are using. You want as much wire as you can get attached to the jack--see the pics below.
Strip the end of the jack's wire. You will notice a wire inside too. Strip that as well.
Tin the ends of the wires.
Solder the wires to the underside of the circuit board. (See below for the details.)
Reassemble the AV pack and enjoy digital sound through a cheap cable!
Pictures & Build Notes (click to zoom)
Advanced AV Pack Mod Overview
Pull out the guts and snip the red wire attached to the red jack. If you want to use the red jack, anyway. Pick another jack if you like. Or add another one.
Advanced AV Pack PCB Connections Closeup
You are looking at the underside of the optical jack fixture. Solder the inner wire of the analog audio jack's wire to the point closest to the edge of the PCB. The outer conductor is attached 2 pins away as shown here.
Note that the inner wire should be connected to the conductor on the inside of the analog jack, and the outer wire should connect to the outer metal shield. This is how my AV pack was, but if you have a multimeter, test yours to be sure it is the same way.
You might need to use some electrical tape to keep things from shorting out. I did because I stripped too much insulation off the ends of the wires.
Advanced AV Pack--Assembled
Put it all back together. (I suggest testing your new coaxial digital audio jack before you screw the top on.) Now go play something loud!
HDTV AV Pack Modification Overview
The same techniques work on the HDTV AV Pack. This time, instead of re-using one of the existing jacks, I decided to add a new female RCA jack. You can do the same: nip the end off of an old cable, drill a hole for it, and make the connections as shown in the picture. Or, just use one of the analog audio jacks as shown above.
Don't know how to solder? This web page can help. Need a soldering iron? For this job, you can probably use the cheapest Radio Shack special. (Be sure to get rosin core solder, not acid core solder.)
Want some cheap Toslink optical cables anyway? Parts Express has them for less than $3. I have several of these and they don't sound any different than expensive ones to me. (Parts Express rules. Get a catalog.)
Looking for a component video + digital audio switchbox? For my gaming needs I narrowed it down to the Audio Authority 1154 (I got mine from Digital Connection), or various models from Zektor (nicer but a lot more expensive). There is a much cheaper option, the Impact Acoustics 3-way switchbox, but it doesn't handle coax audio at all.
A while back I found this MS Word file on an Xbox message board, detailing the Xbox's digital audio pinouts. This is where I got the idea for this mod. Credit to you, Mr. Mystery Hacker.
01/03: First published 02/04: Edits, changed to zoom pics, added info on the HDTV pack, added stuff to links section 04/05: Added affliliate links 06/06: Added link to 360 support. Fixed some dead links. Updated the HD switchbox notes.