From what I know on one stereo input you can connect yamaha 3 zone cymbal pad (piezo/switch/switch). Second approach is using one stereo and one mono input. On stereo goes bow piezo/edge switch and on mono bell piezo (it's piezo/piezo/switch).
If you want to use one surface best way is yamahas system with two switches. Isolating two piezos on one surface is almost imposible.
For some kind of sandwich, multiple isolated zones you can go with two piezos but they have to be very good isolated between each other.
Here is my newest diy 3 zone cymbal pad on which I work this days. Its piezo/piezo/switch system. I use two identic cymbal in sandwich. One cymbal is like base of this pad, and from second one I cut out bell to isolate it from rest of pad. Here are some pics, I'm sorry for my poor description:
![Image](http://s18.postimg.org/fjsc4arr9/Photo0111.jpg)
On base cymbal I glued 2mm soft PVC. From aluminium tin I make edge switch,isolate bell (glued 2 piezos and make distancer from foam double sided sticky tape), put back rest of massacred second cymbal and that is it. Only thing left to do is to glue bow piezo and bow area to the base and some fine rubber on top of whole pad. That's it. Hope you like it =)