X-Fi has newer technology then the Audigy 4 Pro, the X-Fi has CMSS, which enables you to use headphones and you will be able to tell where the sounds are coming from, like having a 7.1 speaker system. It also has the most advanced EAX, which is 5.0 i believe. I have it and i think its awesome, just make sure that you have a nice speaker setup or headphones before you get it. (My $30 logitech one works great).
The $280 X-Fi Fatality features 64MB of XRAM, i read reviews and i personally think that the Xtreme-Music is a much better value ($130) vs the Fatality ($280), and the only difference is the XRAM.