Not sure which Yamaha keyboard you're using. But if you tweak the MIDI IN settings (specifically the channels for chord detect) and change the chord recognition mode to "Fingered" or "AI Fingered", you should be able to control the Yamaha's chordal accompaniment with incoming note messages from your Roland RA-50.
You might have to tell the Yamaha to ignore everything except note messages, so that the RA-50 doesn't inadvertently start and stop the accompaniment with SysEx, etc.
I played my Tyros for years with output from a Roland BK-7m module, because I much prefer the Roland's simplified chord fingering. I understand how Yamaha's AI Fingered works, but Roland's implementation (making the bass inversion an independent setting) is better. Most songs/chords can be played with fewer keys pressed, and you can still easily play slash chords when you need to. My $.02.