PC and Sound System

I just bought a new sound system, as un upgrade from my crappy generic speakers.

There are 5 speakers in total, and a sub. They're all connected up just fine, but when I connect it to my PC (which has 6 inputs for this type of jack) it's only reading from one input. So only 1 set of speakers are being used, whilst my other goes to waste.

What's the deal? Is my computer just naturally been setup for just this one input?


EDIT: Dammit just sorted it. My configuration was setup for Stereo, and not 5.1 sound ><