OK,
DTXpress II (I asked which module because the DTXtreme is sometimes referred to as the DTXTII or DTXv2). It would actually be useful to know which 2 zone ride you have, but I am assuming a Yamaha one. If so, you cannot use 9/10 - you need to use one of the "stereo" inputs 1 to 8. The 9/10 input can only be used with two mono pads.
The stereo pads use a single piezo and rim switch. 9/10 doesn't - it is just intended for two mono pads (one piezo each).
While you say that you have added a Pintech 2 zone pad and get two sounds from a mono cable - my guess is that you have really used a stereo cable, but without the splitter and into inputs 9/10. The Pintech pads use two piezos, not a piezo and rim switch, so need two mono inputs, like 9/10. Sorry if this sounds confusing, but unfortunately it is!
So, if you want to put a Yamaha 2 zone ride into the module, you need to use one of the inputs 1-8. If you are using a Pintech, you need to use 9/10. Other combinations are possible, but it usually involves a bit of soldering etc.
Keith.