I can't tell you anything about the other card but I just bought the same Creative card you're looking at. It's worked great for me. It's got it's own processor, RAM and some nice tweaking features although I find myself tinkering with the speaker system's volume and sub-woofer settings between music and gameing, and even between planes and GV's in AHII. Not a big issue and I'm not sure if it actually stems from the card or the speakers. Either way, two minor tweaks and all is well.
I've read about problems with the drivers but I haven't had any (XP Pro) and I updated to the latest ones. My system is similar to yours (EVGA 780i mobo, EVGA 512 8800 GTS, Intel 6750 2.66 Conroe, 2 Gig Kingston RAM, 250 Gig Seagate 7200 RPM drive...) so it should work out for you (although I think Vista is where most of the driver issues are coming up).
Also, don't forget to disable on-board sound before you install either of those.