Solved the problem ...
... By getting a new sound card.
I'm not sure whether it was software or hardware related, but what the heck.
I'm having the exact same problem with the exact same motherboard, soundcard and games, and also with the new battlefield 3 game.
I will buy a new soundcard to, so could you let me know what card you bought and how it runs with the games you have? Also, did you remove the original soundcard, the SupremeFX II from your motherboard after installing the new one?