Yamaha DTXpress/DTXplorer/DTXtreme

Pete:

You can certainly add another DTX to your kit to add more inputs. I, 
and several others on this board, do just that. One member (OLDGUY) 
even has three DTX modules!!! 

I run my two modules into a mixer, and send one Main Out to the PA. 
On one module I have my snare, bar pad, and bass. I run the Snare and 
bar pad on the left channel and the bass on the right. On the other 
module, I run the tom on the right channel and the cymbals on the 
left. This way, I have four outputs coming from the modules into the 
mixer, letting me individually adjust the volume, gain, eq, etc. of 
each group. When recording, I send these four lines directly to the 
main mixing board.

The one thing you'll need to be careful of is crosstalk between pads 
that are assigned to the two different modules, as there is no way to 
use the Rejection parameters to prevent this.

Hope this helps,
Stephen