Paul, doesn't the X-FI have a music production mode to engage the ASIO drivers?
I seem to recall seeing something to that effect.
I used to have an E-MU0404(PCI) that used the Creative ASIO drivers. I loved it.
However, I don't know what, if anything, the X-FI may have in common with its E-MU cousins.
That said, Tim, you will find that most of us will recommend what we are using. The good news there is that most current interfaces are pretty solid units.
I would also avoid anything Lexicon(severely outdated). the AKAI EIE(red), and anything else with no mention of ASIO drivers in the specs.
I can recommend the Focusrite Scarlett series(I don't own one, but I've played with the 6i6).
I can definitely recommend the AKAI EIE Pro. Very good ASIO drivers, features that set it apart from the crowd, very flexible and controllable, and a certain coolness in its appearance.
I was a bit leery of USB units, but it has massively exceeded my expectations.
Check it out here:
http://www.zzounds.com/item--AKAEIEPRO