Conclusion:
Yamaha PSR s-950 is INCOMPATIBLE with TC Harmony-M "IF" you plan to trigger the harmonies from the right hand chords in real time. There are issues with the sustain pedal operation, as well as a Yamaha "weirdness" that does not play well with the TC in this mode. For simple, arranger play .... it's OK, but I require a more unique approach.
PA-900 ... you're looking better all the time to me.