Thanks. I found that image over the weekend, and went back and checked the wiring. It appears to be correct. Initially, the two piezos were wired to one of the Alesis jacks, with the small PCB. I bypassed that, and wired it directly to a 1/4" jack. Head Piezo goes to the tip, and the rim piezo goes to the ring. Both are grounded to the sleeve.
Still though, when I plug the trs cable all the way into the jack, I get just the rim trigger. If I pull the plug partially out of the jack, so that only the tip connects, then I get the head trigger only. Not sure what is going on.