sorry for the late reply;
It's currently for windows ONLY, I made a Linux version;
But I had it on a Ubuntu PC that want through a GRUB UPDATE
that the BIOS didn't like;
the Universal Version *Should* work with any type even ones not on the list;
the code is pretty simple:
update.cmd (sansa fuze version)
update_files\magic\magic.cmd sansafuze <<tells magic.cmd the "unix name" of your drive.
magic.cmd
@echo off & ECHO RockBox autoupdate & ECHO www.autorock.sourceforge.net & cd .. & cd.. & del ".backup2\rockbox_back.zip" & "update_files\7z\7za.exe" a -tzip ".backup2\rockbox_back.zip" .rockbox\ && del "rockbox*.zip" & "update_files\wget\bin\wget" http://build.rockbox.org/data/rockbox-%1.zip && "update_files\7z\7za.exe" x rockbox-*.zip -y
It tries to backup your current .rocbox folder, then if successful, it deletes a previous update (.zip) file, then it uses Wget to download the lateset Build (not 3.5 or 3.X), If the download is Successful, it will extract the update (7z) and updates your player.
So in short, it can't do any thing Rockbox Utility, cant. but I find it a bit faster for people who just want to do a "quick update."
The Downloads page tells how to work on use on a simulator for the people who want to make SHURE that it will work on their player.
...OK, of topic a bit.
about Un supported builds, I don't know if there stored in the same place as the Unstable/Stable, if there located in the same folder:
http://build.rockbox.org/data/and begin with "rockbox-" and is a zip folder, then get the Universal, and edit "update.cmd"
to Reflect the "UNIX name" ( I use "UNIX name" loosely basically I mean no spaces and all lower caps)
If the updates are somewere else, you will have to edit "update_files\magic\magic.cmd" and make wget"
http://build.rockbox.org/data/rockbox-%1.zip point to the File, and the UNzip command will have to be modified too,
If you get it working you should contribute yours to the project, if you have any other questions feel free to ask.