I use an old P60 piano to control my PSR S910 and it is very effective. I simply assign it to channel 1 and give it “keyboard”. All the functionality of the Psr is available through the p60.
What was a little surprising though, was that when you switch the P60 to internal control, it maps the correct voicing on th PSR. This is not the P60 voices “playing through” the PSR, there is no audio connection, only MIDI.
I’m very pleased with it. Also, the sustain pedal on the piano works on all sustainable voices on the PSR, too.
In addition, I have a KX25 hooked in to play the second voice of the PSR and all the modifiers act on that voice until a new one is selected. Playing live, this is very, very useful for me. It means, for instance, that I can have grand piano selected for left and right 1 with say, nice flute on right 2 and be able to play flute with or without piano on the right with no tortured selecting going on.
I think there is enormous scope for live performances using external controls. I even have a DD65 drum set feeding in to play the style’s kit1. Brilliant, but you have to get someone else to ply the drums if you want it live LOL.
I think this level of compatibility is only possible using all Yamaha instruments, but I may be wrong as the first 128 MIDI voices should be standard across manufacturers.
I hope this helps.