Yamaha DTXpress/DTXplorer/DTXtreme

I know this was asked before, but I can't find the thread related to 
it.  I would like to add more drum pads and cymbal pads.  Can an 
expansion module be used for this.  I understand Roland makes an 
expansion module, would this work with the Yamaha module...have any 
of you folks out there tried this?  I would like your valued 
opinions on this, and what I would need to add on to my system.  I 
want to add  1 or 2 more drums and 1 or 2 more cymbals.  Also, would 
I be able to mount an expansion module to the Yamaha drum rack that 
is standard for DTXII, where it would be next to the DTX 
module...or  would I have to replace my rack with a 
Gibraltar?  I know these are ALOTTA questions, but I feel I can get 
the answers from you guys....thanks for your input!