How much of a shine can you put on $hi+?
the mini-jack line-outs on computers are just about the worst possible construction of an audio system imaginable. The internal wiring is completely unshielded and open to interference from one of the noisiest (electromagnetically speaking) environments on the planet.
There are only a couple ways to get away from that, and they all keep the signal digital until it is far away from the box.
You'd be better off spending the money on an external breakout box (M-Audio or something similar), or a card that does optical out.