Yamaha DTXpress/DTXplorer/DTXtreme

Has anyone used a stereo pad (TP80S, for example) plugged into 
trigger 9/10.

According to the manual, a stereo pad with stereo cable in trigger 
9/10 will have one channel going to 9, and the other going to 10. I 
can't seem to get the pad to trigger channel 10.

I am using a stereo cable and TP80S plugged into 9/10. I have set 
the pad up very similarly to the TP80S snare I have, which 
successfully triggers a rim and snare. At first I thought it might 
be a problem with the stereo cable or pad, but after swapping 
everything out with the snare, the cable and both switches on the 
pad work fine.

How do I get the pad to trigger 1 sound for the rim, and another for 
the head, when plugged into jack 9/10?  So far it will only trigger 
pad 9.

Thanks for any help.

Ian