I have the exact setup you are refferring to and recently had to reinstall the drivers to get them working properly. My suggestion is to do the following:

-Make sure your onboard card is disabled in your bios and uninstall any software for it (i.e. realtek).
-Unistall the Creative stuff (all of it).
-Install just this driver:
http://support.creative.com/Downloads/welcome.aspx
-Install this software:
http://support.creative.com/download...wnloadId=10811

That got my sound to work and the pulldown in BF2 to say "Creative-XFI"