my mp4 version
 

CORE: PMA300_100
DATE:2006-3-15
FW:SRX-3.5.37
DATE:2006-3-24

maradona2007,
It is impossible to tell you which firmware will work with your player and the PMA300_100 SRX-3.5.37 versions are not so common.
I have a player that uses this firmware and also has no radio feature and I have tried many different firmware versions on it but have found no others that work. I have lost track of how many times I have killed it but have always managed to recover it.

If you want to try to activate your radio chip with another firmware you will need to just try different ones and hopefully you will have some luck. Be sure to make a backup of your firmware before you start though as you can bet you will need it.

Personally I do not use the radio feature on my other players as the reception is very poor on all 6 of them and a couple even pick up interference from the LCD which makes them useless.