Apperantly a double flashed 28C256 is a drop in replacement for the old dx7 16kb 27(c)128 Mask Rom!
I used an *Official* TL866 programmer and some knowhow and some stuff from the hacking bench to roll my own copy of SER7
Now to fix the velocity...
~Playin' Those Big Fluffy Pads at the Crack o' Dawn~
Yamaha DX7 > Yamaha SY77 > Kawai K3 > PC via Roland UM-ONE Rev 1.