It's actually not important if your system recognizes the files, the game does.
Just put them in the Gramophone folder, preferably as ogg files (other types can end up only playing part in the game) and go to the radioman's gramophone commands, pressing the 'play' button will start cycling through the files in that folder.
Just look in google for 'ogg converter' if you want to find something to turn files into ogg files. The one I found took a while to convert the many mp3s I had, but it was worth it!
