If you are interested, this YT-vid I founded on Inet:
"
Using Psr Sx900 Style, restyled and new OTS. Both Keyboards are midi connected. Tyros Right123 plays Crumar upper (also harmonie & octaving), Crumar upper plays only his own voice while Crumar lower is connected to Tyros left. …….. "
F.y.i.:
https://www.youtube.com/watch?v=SayE5a5uvpg