I know this is very controversial but my vet recommended a dry, sensitive food to help with Smokey's tummy troubles. He's been fine ever since. Neither of them were really into wet food anyway, I used to chuck loads of the stuff. Now they eat almost exclusively dry with a tin of Applaws at weekends. They drink loads (yeah I know it's not normal etc...) and are certainly not dehydrated. I check their water intake really seriously having lost a cat to crf. Their coats have never looked better either.
Like I said, this opinion isn't shared by many on here but I trust my vet wholeheartedly on this and you can see the difference on the before and after pics of Smokey.
By the way, they're not on s/o, just Sensible 33. Josh was on Mature 27 but they kept eating each other's tea