Need help with my new rig and sound

[Felverick]

I just built a new system yesterday and it operates great except the sound. I'm using the RealTek HD integrated that came with my EVGA 750I FTW board. I have the Logitech Z5500 speakers. I'm not able to get sound on all my speakers when playing games and such. I connected the speakers to the PC with the optical cable. Installing the software on my mobo disk has just basically confused me. I set it up as "6CH" in the Audio I/O. The only thing I could think of would be connecting it VIA the cable connectors.

Any suggestions?

Rig:

EVGA 750I FTW
E8400 Core2 Duo
4GIG OCZ Reaper Kit
9800GT