Hi titetrax,
A friend used one of those SB Xfi cards. There was lots of latency that he could never get rid of and ended up taking it back and got an Maudio Fast Track.
Your Realtek should work fine for playback, but recording will be a problem because of latency.
On my system thete is a very small amount that i can adjust the asio4all buffers before I start to get drop outs.
The Realtek and SB Xfi are reLly designed for playback. They can record, but they were never designed to do so via Sonar or simular software.
Disable your Realtek in bios before installing the SB.
Also, check to make sure you didnt set the asio4all buffers too much. That will cause dropouts.
I'd sell one of those hdd's and get a decent audio card :)
Good luck. Hope some of this helps.
Bub