well for 2.1 speakers you only have 1 thing plugging into your sound card. usually that port is coloured green.. not always tho..
so.. if its anything like the 2.1 speakers i've seen.. this is what you do. you should have a wire that has 2 rca plugs on one side, and a speaker type plug for plugging into your computer on the other end. plug it into that green port, and the other side plug it in that back of the subwoofer (location may differ..) where it says "audio in". so either match colours, or go by right and left. once you've done that, then plug your 2 speakers into the back of the subwoofer. again, either by colour or by right and left. turn on the speakers and test them out.. move the sound bar to one side, and if the sound moves to that one speaker, then its setup right, if it goes to the opposite speaker, then switch around the speaker cables.
i hope i understood what you were asking..
"Is virtue a thing remote? I wish to be virtuous, and lo! Virtue is at hand." -Confucius