Daniel K (a reknowned Creative
driver modder) has made some unofficial
drivers for Windows 7 that restore 5.1 for the X-Fi cards in Windows 7 Beta.
Sound Blaster X-Fi series Support Pack 1.0 Supported X-Fi models:
- Creative SB X-Fi PCI (except Xtreme Audio)
- Creative SB X-Fi Titanium PCI-E
- Auzentech X-Fi Prelude
Here is a link to the Creative forums with info, etc. At present only the MegaUpLoad link is working.
I installed with my Auzentech Prelude and all works as he as indicated. Your mileage may vary

.
Insure you uninstall your present drivers, reboot, then install these.
It is
ONLY for the cards listed above.
As his disclaimer...there are no warranties, etc.