Speaker Setup Issues

[jarofcookies]

I just bought a SoundBlaster Audigy 2 ZS. I have Logitech Z640 speakers (5.1, in case anyone doesn't know). When I plug them into the card, I can get sound from the front right and left speakers, but nothing from the rear or center speakers. It doesn't appear to be a problem with my wiring, though I'd be willing to check it again. I have Orange (center/sub) in line out 3, Black (rear) in line out 2, and Green (front) in line out 1. I've tried plugging them into different places, but it doesn't help (unless I have black in 1, then rear works, but front doesn't, so I know my rear speakers at least work).
Searching the Logitech and Creative haven't given me any helpful information, nor has the rest of the internet.
I'll do anything I can to help anyone understand the problem or whatnot, and if I need to try stuff I already did,  I totally will try it... cuz ya know... It might work.
Any ideas would be apprecianted.

[Windows98]

First make sure you have an updated sound driver for your hardware, secound make sure your sound card can take 5:1 surround sound. 3. Go to audio properties and adjust your computer to let it know you hook up 5:1 speaker

[jarofcookies]

I've updated the driver and made sure it's been told that I have 5.1 speakers plugged in everywhere I possibly could. The card and all the documentation say it's a 7.1 card. Now I can hear from the rear speakers, but I can't get anything from the center speaker.