putting two sensors on one pad? if you put two sensors on one pad, you'd have to plug them into 2 different inputs on the brain to get 2 different sounds from the same pad. and even with that, the two sounds will be simultaneous. i don't see much a point in putting two sensors onto one single pad.
most brains handle sensitivity and can accurately output the volume according to your "velocity" or how hard you strike the pad with only using a single sensor. SO... you shouldn't need two sensors if you've got a good brain.
one of my old drum instructors build an electronic kit using a a practice pad drum set, 5 sensors, and a Yamaha DTXpress brain (i think) and it sounded pretty good. could program several different sounds to each pad and the sensitivity was relatively accurate given the "homemade" kit. =)
Are you wanting to use two sensors to create different "zones" on your pad? Wat i mean by this is say the center of the pad would be zone 1, and the outside edge or "rim" would be zone two. Zone 1 could be programmed as a snare hit, per se, and Zone 2 could be a rimshot or cross stick. If you're going for this effect, then yes, i think you can use two sensors, HOWEVER, the sensitivity of the sensors would have to be crazy accurate as so when you strike Zone 1, Zone 2's sensor doesn't pick up the signal and feed it to the brain, thus producing a snare hit AND cross stick simultaneously. Catch mah drift?
As far as reading up on electronic kits, id check out ROLAND's site and check out their V-Drum section (V-Drums are like the industry leader in electronic drums!), or you could check out Yamaha's website. I'm sure they've got more literature on the subject.
Hope this helps somewhat. Take care.
-Fisher