The Klipsch are suppost to be good, but ive heard of loads of them having to be RMAed after a few months cos of a fault.
The Creative ones, while good as well, will also use the full capibilites of your cards 6.1 output.
If your Klipsch ones are doing you fine w/ no probs, then keep them as long as possible. If not then consider a different set. Ive never heard of probs with creative speakers or logitech.
On the other hand, very very few things will take advantage of the 6.1 outputs. Only 1 film comes to mind, SW:Episode2.
Theres both a chance that 6.1 will catch on quickly, leaving you and you Klipsch in the dark, but theres also the possibility that it wont, seeing as a hell of alot of people own some sort of 5.1 sound system, they`d risk alienating a large market share.
By the time 6.1 takes off, if ever, then your Audigy2/Klipsch will be bargain basement products, so you could always upgrade your sound system then.
Your choice.