I need advice and help. I do NOT want to buy a 5.1 speaker system for my computer since I have an Onkyo HTS760 6.1 system right next to it.

I use a RCA-to-mini cable (what do you call the speaker jack? 1/8" plug, mini stereo jack, what?) and I do not get stereo, I have to plug in either the red or white jack (not both) to get sound from all the speakers otherwise it only comes out on one side.

I need something special to make it work, what is it? I'll buy anything under the price of a MegaWorks system

does your sound card have a digital output?
A single mini-cable to rca will never do 5.1.

My computer has S/PDIF out but my surround sound system already uses it's digital coax connection for my DVD player. It has one Optical (TOSLink) open though. Think I could buy an adapter for it?

SubKamran, I have the same model Onkyo system in my room. I wouldn't recommend you to use the digital out from your sound card to the receiver. If you use the digital out, you will only get 5.1 when you play DVD's with surround sound or play games that have Dolby 5.1 support. I have mine connected from the sound card to the Receiver's DVD 5.1 input. I bought 3 minijack to RCA 6' from radio shack and used that to connect it. That way, even if I'm playing MP3's I still get sound from all my speakers, and surround sound in all my games. My sound card is an Audigy 2, I think Creative made the digital output so that it would only be useful if you had it connected simultaneously along with the analog outputs to one of their megaworks speaker systems.