well it looks like you have tried everything going here, you have doe well to finds as many firmwares as you did
there is one here on the teclast FTP site
ftp://59.39.59.99:2121/teclast/mp3/FW/
maybe have a route around there and see what you can find as they may have some older ones available
i would suggest a quick email to company PASEN, they resell this player and they may know why this is happening, it could be that a hardware revision was made or something like that, anyway a quick as to them my shed some light on the subject sa to why none of these firmwares work
mail address from here
www.pasen.it