I know there are hard foods that he can eat that will not promote the crystals, unfortunately I don't know the names of them. I know there are others here who have cats with the crystal problem, and some have even had the surgery. You can do a search here - probably for crystals - and I'll see what I can find too.

Some PT members who have had cats with crystal problems:
Randi - Randi & Fister
KrazyAboutKats - Tracey & Storm
Cinder & Smoke - Boots
Glacier - Pete
Barbara - Barbara & Tigris