Uh... you already had the speakers and you bought a new sound card, right? It may be a driver issue... have you tried updating?
as you asked, i dont think these speakers are the best suited to your sound card... your card has a snr of 109dB, and your speakers have 80...so you're not taking full advantage of your sound card with that...
In my opinion, if you're no audiophile on-board sound is pretty decent for gaming, music and video.
Heh, you are never going to find "SNR 109db" speakers. Ever. They don't exist. Speakers produce hundreds of times more distortion than electronics at clipping output. I seriously think some of those "SNR" numbers are complete crackpot numbers pulled out of someone's...jacket.
Even very good bookshelves at 90db (1W-input) output will produce around 30db of distorion at from say 20-2KHz. But above that, distortion might be essentially zero. If you took "SNR" to be output over distortion, then the "SNR" would only be around 60db in the bass/midrange areas, but extremely high in the less audible registers. More likely when some companies list "SNR" numbers, they aren't over a wide range of frequencies, but rather at a specific one that makes the product look good. This happens *very* often in home theater, so it isn't limited to PC marketting.
Sorry, wasn't trying to derail the thread. Rather, I was trying to point out--manufacturer numbers often mean nothing in the abscence of third party measurements. Once those measurements are obtained, it usually becomes painfully obvious the specs weren't outright "lies", but just conveniently left out the fact that the numbers were produced in very favorable conditions.
PC speakers tend to be very small, and thus distort naturally from being overworked (fed a ton of power which it bleeds off from compression) and over-EQed (ton of distortion). Get some bigger speakers (with larger drivers). This is probably the most general advice for improving your sound quality at the PC-level. Once you go into hifi with bookshelves or floorstanders, a bunch of other factors come into mind.