It's an old thread, but this suggestion should help new readers:
Recent versions of MPlayerOSX Extended don't work for me.
Use Audacity to read .ra files, instead. Audacity will load the file, and allow you to play or edit it. You can also export the file into whichever common format that you prefer.
I've told OS X to open all .ra files with Audacity, by default, on this box. It saves time.