I just got Rockbox working on my X-Fi, thanks to your hard work. It looks awesome!
At first I tried to build everything myself, and after flashing the firmware.nk file I could get the basic text prompt (I.E. a black background with white text, saying that it was charging). However, when I tried to actually boot Rockbox it would first show the Creative logo twice and then go to a black screen.
Perhaps the build in the git repository is broken at the moment? Your prebuilt firmware is about two months old according to Dropbox. Unfortunately I don't know enough about developing for embedded systems to help you out (or even figure out if there's something wrong at the moment - I have no clue where to start).