The way noise cancellation is done within the headsets is by playing back a sound that bypasses outside interference so you do not hear it. That is done with hardware inside the headset, so I assume that the way the Fatal1ty works is by simply transferring the hardware process into the sound card. I'd also guess that when it comes out it will have dedicated software drivers and the like written to allow the X-Fi to work, making it no different from any other proprietary computer peripheral; or maybe the X-Fi has dedicated chipset instructions specifically for these headphones.
Edited at Wed Jun 10, 2009 2:52:10 PM
Michael: Jodie, how's my schedule look for today? Jodie: You've got a conference and dinner party at the Japanese Embassy regarding wildlife protection. Michael: Oh, yeah...sorry, but I'll have to cancel that. I'm heading out to save America!