Update: Problem solved.
I tinkered around with this a bit more and found a solution. In the "Output Chords on Channel" tab, change the "Note Range to output" on the low end from the default of 36 to 38. (Note: I'm guessing this only works on 61-key arrangers).
Anyway the correct chords are now coming through fine on my S975! I hope this is helpful. Cheers, Gary