Creative Sound Blaster X-FI Xtreme Audio and Linux
Creative Sound Blaster X-FI Xtreme Audio 24BIT Sound Card and Linux are currently a not go. There is no support for any of the advanced features nor for basic sound output using ALSA. The good news is that Creative is planning on writing closed Linux drivers for X-FI, and a beta release should appear around the end of this year.
NOTE: There are rumors of the card working with some OSS drivers, but I have no confirmed it. If anyone has gotten the Creative X-FI card working with OSS, feel free to leave a comment.