You'll find many people with strong opinions on food on our forum.
Personally, I'm feeding an RX food by science diet called d/d feline skin support made from Venison and green peas. This food has cured the terrible patches and raw skin caused by food allergies for my cat Baci. For that food the main ingredients are Venison, water, venison liver and Green pea protein....and yup it smells fairly bad though baci eats it up really quickly.
I'm only writing this to share that some RX foods seem to work and this one has no chicken....though it is not specifically formulated to combat crystals.
Hopefully others will have more specific info for you.