X-fi is still not supported at all under linux, last I checked. Creative plans on releasing closed
drivers but not yet:
The X-Fi series of products are not supported under Linux. (Yet)
Closed-source drivers will be available for the X-Fi series of sound cards.
It looks like the first public Beta will be available end calendar Q3 or early calendar Q4. It has taken more resources than expect to redesign our software and drivers for Vista.
It is planned that the drivers will have full support for ALSA (playback, recording, mixer, MIDI, synthesis) and OpenAL 1.1 (with EAX effects).