My cat Tiger was blocked in 1998 and required emergency surgery. He is prone to blockage and I can tell when he is beginning to have issues because he gets cranky. When this happens I feed him S/D for a few weeks to help break up the crystals. It's important that cats don't stay on S/D. It is only intended for a short period (6-8 weeks I think) and then they should be put back on a preventive diet like C/D or Medi-Cal Preventive. It sounds like Pouncer is on a prescription diet though so you've got that covered.
I hadn't heard of stress causing crystals before but I suppose it's possible. Maybe some Rescue Remedy in his water every day might help.