One thing you might consider is transitioning him to a raw diet--many cat owners report urinary issues subsiding after doing so. Quality pre-made raw mixes are often less expensive than the prescription diets. DIY raw is more effort, but can be fairly inexpensive if you have the time and freezer space for bulk batches. feline-nutrition.org has lots of info about raw diets, and is a great starting point for research. At the absolute minimum, consider a grain-free wet food (if you're not already)--cats are not built to consume grain, so it can cause some issues.
We feed our cat Primal brand raw nuggets. She never had any internal issues, but she was fat and lethargic on low-quality kibble. She lost 8 pounds and gained so much energy when we switched her. Also bonus--her poop doesn't smell anymore!
You also should consider discussing diet changes with your vet. However, some vets are very anti-raw, and some also would prefer you buy whatever prescription food they're pushing. Speak to your vet, but also let your own research guide you.
(...and my first MMM forum post ever is about cat pee. An auspicious beginning.)