To be honest, YES... I DO want to run two arrangers at the same time. Let us take, for example running my G70 for what it does BEST (let's say drums, saxes and E Piano, for instance), and syncing an S910 to it, for what IT does best (let's say the acoustic and electric guitar parts, Bass part, etc.). A combination of what is BEST on each board, rather than pick the compromise you can live with best, and leave it at that...

While theoretically, you MIGHT be able to trigger the divisions with an external piece of gear, it's going to be pretty complicated, as you are going to have to send different MIDI streams to each keyboard, as whatever makes the one keyboard trigger it's division changes is going to probably have some unintended effect on the other arranger.

Bottom line is, this would be a walk in the park if only the manufacturers would pick ONE common set of instructions. No need for complicated external gear. Simply press VAR4 on the one keyboard, and VAR4 comes up on the slave...