Oh the dreaded calcium oxalate crystals. Not to scare you, but those are the hardest type of crystals/stones to combat in cats. Believe me, I know. My 7 year old male blocked with oxalate stones 2 months ago, and required surgery. So since then I've done mass amounts of research on the subject. Bear with me and I'll share what I've learned, so it will hopefully help your cat too.
Oxalate crystals can easily form into bladder stones, and the only way to get them out - is surgery. No way around it. So you definitely want to get these crystals under control, so they don't form into stones like they did in my cat. Oxalate stones are extremely sensitive, and can flare up at any time even on an appropriate diet, much less the wrong diet. The stats of oxalate bladder stone re-occurences are 40% on dry food and 10% chance on wet.
So the diet you feed is extremely important for this condition. Oxalate crystals/stones form in concentrated, acidic urine. So to prevent them, you need to keep his urine less concentrated (with more urine volume) and more alkaline. According to my vet and everything I've read, its best to keep a cat with this health issue pH level between 6.5 - 7. And this is best done with a 100% appropriate wet diet. You do have to be careful of the ingredients, and pay close attention to what you're feeding a cat with these issues. Oxalate crystals/stones can be re-triggered so easily.
Sadly my cat refuses wet, no matter which tricks I try. So consider yourself very fortunate that your cat will eat wet food, because thats extremely important for a cat with urinary crystals. Cut out the dry food entirely and immediately. Its the worst thing that a cat proned to oxalate crystals can eat (Too bad my cat won't believe me when I tell him that!). Also, absolutely no fish-based flavors/foods at all.
I look for foods that are low in calcium, phosphorus and ash. Avoid ingredients such as Vitamin C (it converts to oxalic acid), potatoes and spinach. Weruva fits the bill of a good food for this health issue, but again - my cat refuses wet. But you might have luck with your cat eating it. Also, from everything I've read and my vet confirming it, Wellness is a good food for this condition as well. Its been known to raise the urine pH levels. My vet also told me that high protein foods are best for this condition too.
There are pH test strips that you can buy to test your cats levels at home, to see if the diet you choose is helping (If you can manage to get your cat to pee on a stick, I know I can't LOL).
My cat is currently on a mixture of Royal Canin S/O (yuck), Hill's c/d (double yuck) and I just picked up some Wellness for him. Personally, I would keep him on Royal S/O if he would eat it all the time, but my cat is extremely picky and gets bored and stops eating food all together after 2 weeks if I don't rotate it. While yes, the ingredients are less than par, I have witnessed what Royal S/O does for my cat. And it does indeed increase his thrist drive, which in turn makes him pee ALOT more. I'm talking pee'ing up to 8 times a day, compared to only pee'ing 2-3 times a day on non-prescription food. Royal S/O is formulated to combat both oxalate and struvite crystals. It has high sodium content to drive increased water intake to dilute the urine, which is very helpful in decreasing whats known as the RSS (relative super saturation) of the calcium oxalate stone precursors.
So personally, despite what everyone will tell you on this forum about the poor ingredients (which I do agree, not the best ingredients), I look at the lesser of the evils. Not so appealing ingredients, or risking calcium oxalate stones forming and requiring surgery (again in my case). I would at least keep Royal S/O in the rotation of wet foods. Not necessarily as a sole diet, but maybe once daily or a few times a week at the very least, because it will definitely increase his water intake, which will in turn increase his urine volume.
And I can't stress enough - water, water and more water is very crucial for a cat with this issue. Which is why a fully wet diet is best. If you don't have a pet fountain, I would get one. And leave multiple cold, fresh water bowls in various places around the house. Anything you can do to encourage him to drink alot of water. The more he urinates, the better chances of keeping his bladder flushed out so the crystals don't form into stones or re-block him. Also, I use distilled water only (per my vets recommendation). Depending on whats in your tap water, it can have high minerals and such that can also trigger calcium oxalate crystals/stones. Likewise, bottled water can as well. So distilled water is best.
Sorry for the overwhelming amount of info. It took me weeks/months to dig it all up. Vets sure aren't very helpful. So hopefully you'll find all of this info useful too. Good luck.