Oh poor Dakota.

Fister had stuvite crystals, and as you may remember he had the big operation. Hills S/D are the ones which are supposed to dissolve the struvite crystals and C/D are supposed to prevent cats from getting them, but since Dakota has another kind, I'm afraid I can't give you any advice really.

I don't know what PU surgery is, but if it's the same Fister had, he should not be in danger of blocking up again.

What did the vet suggest?

I hope Dakota will feel better and thrive on the diet you and your vet decide! Keeping all fingers and paws crossed for him.