All inputs 1-8 on the original DTXpress are dual zone so the PCY135 should work. The PCY135 manual recommends setting the GAIN in the TRIGGER menu so that it registers 90-95% when hit hard (for the DTX series). You also have the adjustment pot on the cymbal itself so it is worthwhile adjusting that as well (there are no recommendations in the manual as to what to set it to!).
On the module, make sure the PAD TYPE is set to one of the dual zone cymbals such as PCY Crash, PCY Ride. If you are still having problems, try the "misc" pad types such as "misc 2" "misc 4" or "misc 6".