No sound out of center speaker

Hi, I'm new to this forum so please bare with me. I have just installed a Creative sound blaster live 24 bit sound card and everything is working apart from the center speaker. I've installed all the latest drivers etc and made sure that windows is set to 5.1. All the leads are in the correct holes and every diagnostic tool that I've run says it's all working fine. When I run a speaker test from the creative speaker settings menu I get lovely crisp sound from all of the speakers apart from the center one, which I get a muffled voice saying "center speaker" from the sub woofer. I've looked at the creative help site but it's not a lot of use really. My specs are as follows:
Intel Pentium 4 Prescott @ 3.2ghz
1024mb ddr pc3200
Asus P4S800D-X
Geforce 256mb 6600
Windows XP Pro SP2
My speakers are - Packard Bell Theatre 5800 (on the front of the sub woofer it say's "for AC-3 dts"
Can someone please help, Thanks.