Well I have a Creative X-fi Platenium series for the sound card. So I'd say (without being an expert) that the card is more than capable.
However I am not using the PC for my primary source of Audio. The new Pioneer head unit takes any sound from the PC as an AV-in.
I would use the headunit primarily for the sound either via the Hard drive, Ipod, cd etc.
The PC has pretty much been made redundant but still a cool feature to have as I can use the Wifi on it to surf the net etc.
I was told that a reason to why I have seen gains from the headunit is that the voltage out is higher than a PC soundcard. I dont understand this myself just passing it on!