Mrki, have you tried the firmwares on this site here:
http://www.mympxplayer.com/dload.php...gory&cat_id=15
Also, try
http://s1mp2.org ...they have the board id's so you can try matching up your board id and see if you find a compatible firmware.
Also let me know what version your original firmware was.
(Most likely it was 3.5.35 or 3.5.37)