Hi Mike and Paul --
Guys, guys, I think you're wringing your hands about this a little too much.
The implementation of stereo tone generator channels is a fundamental feature of the SWP70 tone generator IC. This is clear from looking at the Montage service manual and the Montage specs.
The hardware tone generation micro-architecture (based on SWP70) is the same in Genos, modulo differences in wave memory. Thus, I've never really doubted that Genos has stereo tone generation channels and 128 voice stereo polyphony on the preset side and 128 voice stereo polyphony on the user wave memory side.
Yamaha is totally mum about the tone generator IC and hasn't even revealed the chip name "SWP70" in public. I seriously doubt if they will ever say anything much about it except that "It's new and wonderful."
That's not a slam on Yamaha; they have eager competitors.
Counting polyphony may or may not be as straightforward as you would like. Taking Montage as the example, the newest Montage voices are probably "native stereo" and require one stereo channel, i.e., one stereo voice of polyphony. Some legacy Motif voices may still require two channels (each channel panned hard right or left) as this was the way in olden times. The authoritative source in Motif-land is the Data List PDF which has an Element count for each voice. This info was dropped and is no longer published in the Montage Data List. I suspect that Genos has the new vs. legacy voice issue, too.
It's a fun subject, but the picture is soft-focus and not likely to get any clearer...
-- pj