As of kernel in Ubuntu 11.10 (at least as of late 2011 updates), XFI USB (and Titanium HD support) is there.
However for whatever reason, it’s disabled by default as a preference/rule in /etc/modprobe.d/alsa-base.conf, and doesn’t show up in listed devices nor does it play.
Had to go in that conf file, right near the bottom or find this:
“# Keep snd-usb-audio from beeing loaded as first soundcard
options snd-usb-audio index=-2”
… and change the -2 to 1 (being an index for device). This allowed both my on-board Intel audio (index 0) and USB xfi (index 1) to show up at the same time.