i have the XFI-Xtreme gamer i did have an issue with it, when i first put it in it worked great on my win7 ultimate.
then i reinstalled my system and the system didn't recognize the sound card at all, i tried installing the drivers but still no card showed up. i removed it. installed windows again then 1s it was up and running replaced the card and it worked straight away.
the next time i reinstalled i left it in and it was fine, it picked it up straight away...
so just so you know if your system doesn't see it after install, remove it and try again.