Trying to connect new computer to old sound system

[animusbrief]

I am trying to connect a Z68X-UD3H-B3 mobo mounted in a Corsair 500r case to an old Philips surround sound system (MX3900D). I tried to run an optical digital cable from the computer to a small converter which supported the digital coax that my system has. $50 later I still have no audio. I thought toslink was the same as digital optical but I have no clue what I'm doing. Will someone please help me figure out what I need to do to get the best sound available with my setup? Thanks ahead of time...

P.S. My sound system has no HDMI.

Edit: I want to use the SPDIF out port on the computer, but the system doesn't have the same port. The more I read the more it seems like I'm trying to connect a cable that transmits light to a port that receives electricity. If I say @#%@ it and just go with RCA cables, which ports do I use on the back of the computer as there are six? They are...white/black/orange and pink/green/blue.

 

[animusbrief]

Ehm...after fooling around with this for a while, I stumbled upon my solution. As a newbie, I convinced myself I had bought the wrong cables and what I was trying to do was impossible. Thankfully, I'm quite stubborn.

I noticed that my sound system recognized the input: there was no scrolling text telling me no input detected, so I assumed the opposite was true and the signal was reaching the speakers. So, I looked at the computer for the problem. Easy enough to rule the hardware out when all I have is one digital audio port. Next up was software.

It took me a while to realize, but in my sound manager (Realtek HD Audio Manager), there is an option for audio devices that I was messing around with earlier. It turns out I had disabled the optical device, so I just had to right click and click "show disabled devices." Seeing it was disabled, I enabled it and tried again. To overwhelming joy, I now have crisp and clear surround sound. No more splicing cables into the AUX port for me. Consider this closed!