My first experience with 5.1 surround on my computer was a few months back when i purchased the Logitech z5300 thx speakers. Initially, I was blow away by what I was missing out on, especially when gaming...Now comes round 2, in which I've moved my logitech set downstairs (to the new room) and installed my newly purchased Klipsch ProMedia 5.1 Ultra's on my workstation. The install took a while, but was definitely worth it since i was able to used my own speaker wire (monster xp flat) and mount the rear speakers on stands!
Now on to the performance...All I can say is, Holy ***! My Logitech's sounded great, but in comparison to the ProMedia's, great just doesn't cut it anymore. The fidelity and range of these speakers are superior to my previous set in every way, it even has a built in processor for mixing stereo signals to all 5.1 channels. For my logitech's, I could do the same thing but it required using a special setting on my Audigy 2 zs card (cmss 3d stereo surround). Granted, the klipsh are over $100 more expensive than the z5300's (which is why I didn't get them before), but in this case, you're definitely getting what you pay for.
In the words of the infamous Ferris Bueller...If you have the means, I highly recommend picking one up.