Connecting Racing Seat with Speakers to my PC

Hi all,

Hoping someone can help me with this...

I recently received a sim racing seat/rig as a gift (Viper SR600) and I am trying to connect it to my PC to take advantage of the built in speakers when I run iRacing.

The rig comes with left/right rear speakers (top of the seat, behind your head) and left/right front speakers (by the pedals), and a subwoofer in the seat itself... assuming there's also another speaker in there for the center channel, but not really sure...

I am not great with audio, so hoping I am just missing something. Small cables run through the tube frame of the rig and connect together (two sets of cables from the front speakers connect to two cables in the middle of the frame, and then three sets of cables connect to each other at the back of the seat base). On the side of the seat, there is a line in jack, a line out jack, and an AC power jack.

My computer's sound card is capable of 7.1 surround sound. I have on the back of the PC 6 1/8" jacks.... gray, black, orange, green, blue and pink. The manufacturer of the seat provided me with one male/male stereo cable, and a stereo to two female RCA adapter.

In order to get the surround sound (L/R rear and front, plus center and sub), I need to have three lines coming out of my PC, right? So how do I take those three lines coming out of the PC and put them into one 1/8" stereo jack in the seat?

I am so confused! Thanks for any help!