I own a Auzentech Forte. Great sound card with built in amp.
I also own Audio Technica's AtH -AD700 (these are the go to headphonse for FPS gaming). These are extremely comfortable, excellent range, excellent sound stage for gaming, just a little lacking in bass. I find if I set my Forte to +12 DB and cut off at 30mhz they are really good.
The Forte lets you hook up both 2/2.1/5.1/7.1 and headphones simultaneously, so you dont need to be switching jack all the time. Just make sure to go into both the Auzentech and Creative labs control panels and disable the auto headphone switching.
EDIT:
The creative cards using a 3D simulation called CMSS-3D. To me, I find you get better 3d position results with the 3D simulation paired with good headphones than you get with a 5.1 set.
check out the demos on this page. It give you a good idea of the "in-game" 3D simulation the card provides.
Sound Blaster - X-Fi CMSS-3D
The only complaint about headphones vs gaming headset is there is no mic, I personally installed one on of my own. It was a bit of a PITA and would suggest just buy a clip on mic like this one.
Mini Clip-on Microphone - Free Shipping - DealExtreme