Hello duderiffic,
Well - I have done exactly what you are trying to do. I have a VW box in my Volvo S80 working from the HU-850 head unit - now running for the past two weeks. BUT - I have not quite finished. Everything works, but I am debugging the wiring to get rid of some interference from the alternator. This is related to the grounding and highlights the fact that the VW and Volvo boxes though similar are not exactly the same. However I think this will be possible to fix.
I am posting progress reports on the Swedespeed forums at the moment. I hope to have this all finished in a few more days. When done, I will also post some kind of description on this site if I can.
Regards,
Les.