5.1 surround sound system problem

Hello, i came across an old Teac PowerMax 1000 5.1 surround sound system. All the 5 speakers conenct to a subwoofer, which in his turn has a 2 x cinch audio outs. My motherboard is Epox 8rda3+ and i don't have additional sound card, so i conenxted the surroudn system and the PC with a 2 x cinch -> 3.5mm stereo plug and pluged it in the Line out jack. but when i turned on everything i was slightly diappointed - i hear sound from the front speakers and the subwoofer only. All the speakers and cables are working, but i doesn't hear any sound. Does anyone can tell me how can i try and solve the problem. thanks a lot in advance

soon i'll add it

there are 3 pairs of cinch connectors in the back of the woofer - Ouput1, Output2 and Ouput3. So I need 2 more cables if I have understood correctly. I'll take one more today to see if there will be any change.

Here is my PC ...
epox 8rda3+, amd 1,4ghz palomino, Pc3200 256mb kingston, 80gb DM9+ 8mb, 7200rpm, 10gb dm7, GF2 mx200 32mb ... almost for the rubbish but i love it