Ok, thanks to some info from Gimli, I now have sound working on my v1.6 Xbox under Linux. I'm going to spend tonight implementing some changes in magic so that Gentoox will support v1.6 Xboxes. Let me know if I've broken anything! Thanks!

*Update*
Well, its all working fine here... numerous changes have had to be made to my i2c tools, the major problem now is that temperature cannot be monitored because it has either disappeared, or moved. "xboxtemp" will now report "??" as the temperatures and fanctl can only be used to set the speed in a one-shot style. The fanctl rc script has been updated to accommodate to this, there is now a ONE_POINT_SIX variable which can be set to 0 (off) or 20-100 (fan speed) which is executed on boot.

Anyway, heres proof that I have it all running.