Well you can use TINRA to get it into AVI. Once in AVI it should be relatively easy to get it into MP3. Whether through Goldwave or TMPGEnc.
TINRA stands for This Is Not Real Anymore. It’s the only one I know that works. Now be prepared for very large AVI files. I converted a 4398 kb rmj file to a 45818 kb avi file.
Oh, you may have to rename the .rmj file to .rm At least that’s what I did.
The only thing I hate more then real files are .mov files. But I got that down too 