Well, I just tried that setup, and it doesn't work at all. It'll get a few screens sometimes, and the genesis will freeze up, and there is no thing but a buzz that comes through both the MOL and MOR. Are these really for left and right output, or are they a digital signal or something else?
I checked, double checked, and triple checked the connections, and it's all soldered and connected correctly. So, I guess we just need to find where all of the connections turn into analog, and somewhere before it is being amplified. I wonder if it would be somewhere else on the chip, or another place on the circuit board.
UPDATE: If there is an analog signal on the MOL and MOR, then I'm guessing that you would have to cut those two connections from that chip to the circuit board, but if mask of destiny is correct, and the PSG sound isn't connected to it, there would be two problems. First, you would cut off any/all sound to the rest of the circuits, atleast from the yamaha chip, and secondly, you'd miss the PSG sound. In other words, you may get FM (and PCM?) sounds from the yamaha chip , but not the PSG, and no sounds from the headphone jacks or from a DIN A/V cable connection, without adding toggle switches atleast.
I'm not even going to try try disconnecting those pins and adding toggle switches. Using the headphone output is better than that choice, and you never know when/if someone will figure out where to get the analog stereo signal that I'm looking for. Maybe these threads will find their way to some electronics/technical buff that will already know or will start working on it.
The next mod should be to do a built in power supply mod :/