Why not u just get a wire that can split the audio cable into a left and right channel, then from there, get those normal red and white cable, connect to ur a better amplifier?
i do tht last time, cos i using a set of Infinity premiers, 1 12" infinity BU120 subwoofer, 2 power amps, 1 pre amp, then just input the the soud back into the amps and play the sound out, it is nicer

alternatively, just go to simlim, get those normal 5.1 for computers, i using that but if u listen too loud, the speakers cannot really tahan.....but for u i tink it is ok, cos i listen to techno and eurodance more often
or try to change the equaliser setting in ur computer first before buying anything, maybe it is the sound equaliser that is messing around