Dan, if you can successfully remap Yamaha Mega-voices, I would SERIOUSLY take a look at offering your software to MotifXF users. The combination of FULL mega-voiced styles with the MoXF's chord following arpeggiator would be a VERY powerful combination.

And, I would still take a serious listen to default sound and effect balances. There is room for improvement, I think, with those offsets. Essentially, you plug a Yamaha style into the Ketron player, and at least the BALANCE and reverb and chorus depths should sound as close as is possible.

The proof of the pudding is taking a stock, default Yamaha style (no user tweaks, stock Tyros Part settings) and playing it untouched into the stock Ketron module. If you can get those parts to 'sit' right and have the same degree of 'space' around them, you are on the right track.

Give that MotifXF suggestion a serious think, though. I honestly believe half of us here would happily step up to a WS, if we didn't have to leave TRUE arranger capability behind to do so...