Use the default WDM driver
that is automaticly used for Vortex based cards. Get into your registry
- HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServiceswdm_au8830Customization
create 2 new DWORD keys in the above registry entry. DetectSpdifOut (decimal
value 1) EnableSpdifOut (decimal value 1). 
As well, there's a slight problem with
the drivers: the volume is way too low, even with all the sliders turned
all the way up. It's all right for everyday games and apps, but it's
invariably going to cause a problem for some people. For me, I need the
SPDIF to record to minidisc, and I can't do that now because the volume
output levels aren't high enough.