Quoting Diki,
"BUT... what if there was an "Arranger Mirror' channel? In other words, send the arranger ONE MIDI channel, from top to bottom of the source keyboard, and have the arranger itself map those ranges, controls, destinations, all that other stuff, JUST AS IF IT WERE LOOKING AT IT'S OWN KEYBOARD.
There is a very similar function on my K2500. No matter how complicated the Setup, eight zones, multiple destinations, controller mapping, velocity cross-splits, you name it, if you send the K2500 ONE 'dumb' MIDI channel from another keyboard, the Kurzweil maps all those splits and everything to it. It basically just treats it as if it were the raw input from it's own keyboard.
Now this, I imagine, is probably VERY easy to do. The arranger already is doing this to it's own keyboard, all the code has to do is do exactly the same to a MIDI input of ONE channel only. Simple, no?"
That can be done already(talking Ty2).
There are default midi templates that are setup for Ext. KB control or if you want something more special you can edit them yourself.
In fact even using the OOTB default "All Parts" template, if you connect a controller KB set up to transmit on ch1 to the midi-IN B port of Ty2 that's what you get.
You can also play a single midi track into Ty2 (setup in Keyboard mode) and it will treat it in the same way as if a pair of hands were playing the keyboard directly.
Which has all sorts of implications- if we can think of a good use for it!

John