the 5.1 is better if you can afford it. 5.1 true dvd experience. btw the 5.1 isn't just a 4.1 klipsch with added speaker

digital volume readout, headphone plug, dual 8" sub etc etc etc
stealing from another thread
"There are a couple of other minor but none the less important changes from the klipsch v2.400 / 4.1 to the klipsch 5.1 ... Besides the things that were already mentioned: that you get the center channel, an the amp boost to the sub goes from 160 -> 200, and the amp has to provide an extra 60 for the center (total of 500 watts), and the Dual 8" sub (which makes a bigger difference than you'd think) ...
You also get "normal" speaker wires with banana plugs, which stops the annoying static and loose connections from the old miniplug style, the satellites are actually different than the klipsch 4.1's which is said to have an impact on sound quality, and additionally the klipsch 5.1 has a much more polished and professional feel to it. For example, you don't have 3 wires coming out of the back of the control pod, 2 of which go into the soundcard. You instead have 3 miniplug jacks on the back of the subwoofer, and you use the included wires to plug into your sound card (that way if you ever lose the wires, or the wires get damaged, you can easily just replace them).
Just my opinion on the klipsch 5.1 (I happen to own a pair of the v2-400's, 4.1's and the 5.1s)... If you listen to a lot of music, watch a lot of DVDs on your PC, and care a lot about the sound quality for games ... definitely make the investment in the klipsch 5.1s ... Once you get them, you'll never want to go back to some of the cheaper solutions. However, the klipsch 5.1 at $399, or even $375 is not for everybody.
"