Go with the X-Fi with its support for EAX 5, a 'crystalizer' (that you can scale or turn off', support for more voices,
you know what, just go to the creative website and you'll see why the X-Fi is so much better than the Audigy's.
The only thing that you won't get with the XtremeMusic that the Audigy 2 Platnum has is the console or drive bay thing. the only reason you'd use that though is if you hook up an amp, guitar, turntable, or other stuff to your computer. but for listening to music and games, the X-Fi is better.
I have a freind with an Audigy 2 and X-530's, and I tell you what, my X-Fi and X-530's sound better in both games and music.
look at reviews, they all say the same thing, if you don't have an Audigy 2, there's no reason not to get an X-Fi if your upgrading.