Yamaha DTXpress/DTXplorer/DTXtreme

Anyone know much of the innards of the Yamaha DD-55 toy (the silver 
thing with 4x5" and 3x3" pads)? Since I have one of these and given 
that it's MIDI-enabled, I am eyeing it for some surgery to use in 
conjunction with the DTXP2. . It's too big as it stands to mount on 
or near my kit (and looks a bit Flash Gordon to boot), but I am 
minded to take it apart to see if (a) I can mount the triggers 
and "brain" separately and give myself seven additional pads 
reasonably cheaply, and (b) if the pads actually use piezos or FSRs, 
see if I can trigger the "brain" with external pads.

Clues, anyone?

Stewart