www.3dsoundsurge.com is a good place to go for multimedia speaker reviews.
The VideoLogic DigiTheatre DTS are the best now, and likely to stay that way for some time. I obviously haven't seen a review of the Klipsch 5.1 but I haven't heard anything about them that gives me any reason to believe they would perform better than the DigiTheatre DTS.
The Sirocco Crossfires (4.1 version of the DTS) are both louder and more accurate than the ProMedia 4.1s, and I expect the same with the DT-DTS and the 5.1s. Of course, the DigiTheatre DTS are ridiculously expensive, you could get a pretty decent Home Theatre in a Box setup for the price (I believe the same is true of the Klipsch 5.1s which are going for $400 I think? Still less than the DT-DTS...but alot nonetheless).
And really, that's the best way to go, no computer speakers are going to stand up to a real reciever with proper loud speakers.
If you are looking for something at a more reasonable price point the Midiland S4-7100Plus and S4-8200 are both attractive packages for the prices...around $150 and $200 US respectively I believe.