I had the exact same problem and tried every possible solution for my x-fi extreme, it worked fine under xp32 with 4gigs of ram but as soon as i moved to vista 64 the problem occured. I was not willing to loose 2 gigs of ram so decided to put my old audigy2 zs in which works but i cant get surround sound it all comes through the front speakers, in the creative software for selecting speaker set up it is blank

. So i am now looking for an alternative to creative. Any ideas?
here is my set up
Dell 710 xps
Intel(R) Core(TM)2 CPU 6600 @ 2.40GHz (2 CPUs), ~2.4GHz
4 Gigs DDR2-SDRAM PC2-5300
NVIDIA GeForce 7900 GS x2 Dual
AGEIA PhysX 100 Series PCI Card
Creative SB Audigy 2 ZS (X-FI removed after vista install)
NVIDIA RAID Stripe 500 Gig (Dual HDD config)
Creative Inspire T7900 7:1 Speaker system.
Logitech G15 (Blue) Gamers keyboard.
Logitech MX518 Gamers Mouse.
Saitek Cyborg Evo.
Vista Home Premium SP1 x64