I haven't picked up Soldier of Fortune II yet but from what I heard it's pretty awesome.
When comparing the SB Live! 5.1 and the GTXP I have come up with a few observations. I think when playing music the SB Live! is pretty decent. The GTXP brings out the highs a bit better and they are a bit less tinny. For games, however, the positioning is really tremendous. It really brings you into the game a whole lot more. Furthermore, the sound effects are a lot more realistic. At first I was disappointed because the change was so drastic. But after playing MOHAA after a while, I discovered that the subtle little sounds like footsteps come through much more clearly and realistically. I wasn't used to that with the SB Live!
I'll be trying out other games, but so far I am very happy with the GTXP.
To start press any key. Where's the "any" key? --Homer Simpson.