GoldenZero , the ATJ2091 uses the v9.0.xx series firmwares, which is available here
http://www.mympxplayer.org/actions-9...mare-dc37.html
However, those firmwares in the downloads section are for players with colour screens. You can try them though, but might not work properly for your player.
Another alternative is to go to S1mp3.org, as your firmware might be using the pen-style player kind, which they might have more firmwares on.