Hell, what, are you people kidding... Counter-Strike?
Most of the sounds for Counter-Strike are 8-bit 22Khz mono PCM. I mean **** an M-Audio revolution for that?!
And you wanna use headphones too, which means you don't even need to worry about surround sound. Well if you do care at all about surround sound, don't get an M-Audio, as I can't convince mine to play the rear channels from Counter-Strike (works fine with everything else). The Sensaura/Game Mode with the M-Audio is a joke, it introduces a delay of at least 200 or 300ms into the sound. Don't think of using a Revolution for gaming.
The thing with Counter-Strike specifically is you want to avoid EAX if possible.
EAX (the version used in Half Life, anyway) amounts to nothing more than altering the sound depending on your location in a map within the game. I.e., inside a tunnel, add echo. It also allows for basic 3D positioning.
This means you want a card which supports A3D version 2.0, which is the other technology Half-Life supports. A3D is far superior to EAX; it uses a much more sophisticated engine which takes into account the position of the sound rather than the position of the player (unlike EAX). This means sounds are softened by walls, etc. A3D also has the strange advantage of being more sensitive. You will hear an enemy's footsteps before he will hear yours if you use A3D and he uses EAX.
Unfortunately Creative bought A3D and shelved it a few years ago, to remove competition to their EAX. This means the only cards you find nowadays support A3D 1.0, not 2.0. You need 2.0 for Counter-Strike.
There are some cards around which do support 2.0; you'll have to look on the 2nd hand market. A search on this board might yield which cards; otherwise someone else may know.
Oh and Counter-Strike tends to suffer from low-bass, so if you're looking at other headphones make sure they give good bass. Using an equalizer to turn the bass up may help a little too. Forget worrying about fidelity, the weapons sounds in CS are anything but realistic (although various customizations can help).