Problems getting surround sound to work on PC

[pitfall317]

I bought a Turtle Beach Riviera 5.1 6 Channel PCI Sound Card for my new PC. I hooked up my Logitech X-540 70 watts 5.1 Speakers.

Here's the problem. When I have all 5 speakers plus the woofer plugged in and run the surround sound test I get no sound from the back speakers. During the test when it gets to the back speakers the "voice" comes out the front speakers. It's like the sound card only recognizes the 2 front and center speakers.

Only once did it recognize the back speakers. When I tried running the speakers using the default sound from the motherboard I got no sound whatsoever.

I'm not sure what to do here. I specifically bought the Turtle Beach because it's supposed to work so well with my speakers. I'd appreciate any advice anyone can give. This was my big time gaming system and I really want to get the surround sound working!

Here's my computer specs:
Vista 64
Intel Core 2 Quad Q9300 Yorkfield 2.5GHz
BFG Tech BFGE981024GX2E GeForce 9800 GX2
GIGABYTE GA-EP35-DS4 LGA 775 Intel P35 ATX
Turtle Beach Riviera 5.1 6 Channel PCI Sound Card
Logitech X-540 70 watts 5.1 Speakers
G.SKILL 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) (2 sets for 8 GB total)