Hi Technics almost had it before pulling out of the music industry as all the last generation of instruments, keyboard ,organ and digital piano shared the same mother boards so to make a multi keyboard in a module form would have been easy.
If you have a good midi spec. master keyboard you can use a lower keyboard(midi type)set up to match play the lower part on your master keyboard,with the lower part set to external note inf you could also triger the auto accomp,if the midi keyboard can be split, using two channels you could have the set up like those of the Wersi organs,I think you would need a master unit with 128 note poly for this to work for pro use,all voicing could be set on the master keyboard using panel memories provided they are able to store midi set ups like on the Technics KN7000, as I have not had any time on the Tyros I can't comment ther but knowing Yamaha I would be surprised if you it was not able to operate in a like set up. Don't forget the new top of the range Arrangers are very much the same as the workstations we had in the 1980/90s
Food for thought!!!! Regards John.