Here is my setup and review of the SPD SX PRO, using every external trigger input! I am using the following pads and connections.
Roland VH-10 Hi Hat (Dual Trigger)
Lemon 13 inch Snare (Single Trigger)
Roland KT-10 Foot Pedal (Single Trigger) - Yamaha KU100 as seperate output for double kick
Roland PDX 8 - (Single Trigger)
Roland PDX 100 - (Single Trigger)
Avatar 10" Cymbal Pad (Dual Trigger)