How do I hook up surround sound to my computer with only 2 jacks on the back of my computer? ?

Question

I already have 2 pairs of stereo speakers. I have a 5.1 surround sound card. The other jack is for non-power speakers (i.e., headphones, MP3 speakers).

Answer 1

Some of these cards repurpose the mic-in and line-in jacks for rear and subwoofer connections.  You set this up in a control panel for the card.  You need to consult the manual.  

Answer 2

Are you sure one of the ports it is not a s/pdif (coax or optical) port? This is the most common way to output 5.1 (It is usually Green) to an AV receiver.

I doubt a simple PCI card can drive 5 speakers (not enough power).