Thank you for the quick reply.
Check out this url for instructions on porting Genesis voices/instruments to VOPM:http://www.ocremix.org/forums/showthread.php?t=4619&page=2
The process is described by "DXFreak".
And yes, OPN and OPM are quite different chips - not many people recognize that but if you listen to Genesis ports of OPM games (Roadblasters comes to mind) it sounds like a crude toy compared to the beautiful music of the arcade game. I could not imagine the music of Peter Pack Rat ported to the Gesnsis in a million years. Just messing around with VOPM has really lead me to appreciate the chip as a musical instrument - it may not be as flexible or as powerful as the DX7 - but it certainly as a clean clarity to the sounds and can produce very interesting sounds. And being able to discover patches from arcade games for me would be a very powerful tool in learning FM synthesis.
Right now I think adjusting the CYM-logging code in ym2151.c in mame is my best bet. Right now that logging is just crude register dumps - I don't quite understand how it is supposed to be read and how all the VOPM settings could be interpreted from it. I'd rather make huge, ugly logs that say things like: C1/TL = 0, M1/TL=23, M1/AR=31 ... etc etc.
I am not looking forward to this process by any means - but the cym logging looks totally undocumented ... hence my attempt to ask for help here.