The only advantage to having more than 2.1 is listening to music thats recorded and mixed to 5.1 or 7.1 which is only available on a DVD/Bluray music video Discs, a DVD audio disc, and or a Super Audio CD which the later 2 are woefully unsupported the only ones I own are the 2 latest albums by Dimmu Borgir and Metallica's Black Album all three in DVD audio which supports a much higher bitrate and simply sound amazing much like the lossless audio on bluray discs. Hopefully in the future, the CD will die off and the DVD audio discs will become more available. also I you want to skip using PC speakers while they are a cheap solution check out what
http://www.parts-express.com has I've ordered speakers form them in the past for home theater projects.