I've been eying the Tritton surround sound headsets for gaming for their audio controller. Over the weekend I found a guy selling just the controllers on Ebay.
The AX360 has coaxial and optical in:
http://cgi.ebay.com/ws/eBayISAPI.dll...m=220896453137

The AX Pro only has optical in, maybe other differences too:
http://cgi.ebay.com/ws/eBayISAPI.dll...m=320798504848

Hopefully I'll get them soon, I ordered one to use in my home Z5500's to replace the pod, and the other to get 5.1 when I get around to building my car PC.

I'll post up how it works when I get it and hook up my home speakers.