Yamaha DTXpress/DTXplorer/DTXtreme

Hello all,
For xmas today my wife bought me the lovely DTXpressII kit.  I had 
mentioned to her in passing that I was considering buying an 
electronic drum set, and (surprisingly) she hooked me up.  Admittedly 
I had been looking at the Roland kits and wasn't really aware of the 
Yamaha.

Trouble is I'm wondering if the Yamaha is what I really want.  I'm 
not finding much information on the 'net about any expansion 
possibilities, like if I want to add a ride cymbal or additional 
toms.  I'm a beginner so I'm sure this'll do fine for now, but what 
about the future?

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