After a good week of struggling, I found on a Polish website the RIGHT firmware to recover my ATJ 2091N -based Monochrome 2GB MP3 Player with FM radio. This firmware is NOT YET present in your Downloads, so you can add it if you find this useful (I don't know how to do it by myself)!
This is this one:
http://w14.easy-share.com/11391971.html
If you find a way to modify the HORRIBLE boot splash screen, please let me know Wink