Upgrade my computers audio capabilities?

sound card barely effect a 2.1 system because it's still a mono jack that yield a stereo output, what you need to do is look around for a good deal on a 5.1 or 7.1 or the hard to find 9.1 system which has 6,8,10 speakers, then a good sound card will have effect on the music output quality, now a days a good 59 bucks can get you a decent creative xifi (not sure about the name) HD soundblaster card with 7.1 support. Also look into a decoder, that's something you want if you really want good music.