Disklavier

Is the tone generator really XG with more than 600 voices or tones 
or just 128?

Does it need an XG ON message or some manual setup to use the other 
banks?

 

I have tried on MIDI channels 3 to 16 to change banks using cakewalk 
with no difference in the sound.

 

I downloaded the XG PDF manual from Yamaha and every thing works 
fine with the S-YXG50 Software Synth, but not wit the piano Control 
Unit.

 

Maybe the control unit is not XG, can it field upgraded?