So...OK..what I may want is a T4 WITH a Kronos Rack???

Whoops...on second thought until Yamaha (maybe never) gets the MIDI implemtation up to spec...it would be a PITA.
You can't even select sounds properly on the Kronos from the T4.
I know because I tried it with my T2 & Kurz. years ago.
The user voices SHOULD allow one to set MIDI bank/prgm chg and have a external/internal/both setting per voice. Like the Korg PA.
Easy to do...