My 17 year was recently diagnosed with chronic kidney disease. She's on the KD diet. She gets both the dry and canned food because she won't eat canned food that been sitting out, and she eats small meals. So, I leave her the dry to snack on during the day. When I get home from work, I give her the canned a little bit at a time. My younger cat always tries to get into it, so I give her own canned food at the same time. My vet said that the canned was preferred, but it was more important for her to eat, and if she won't eat enough of the canned then supplementing with the prescription dry is the best alternative.
I found a lot of useful information about chronic kidney disease at Tanya's Comprehensive Guide to Feline Chronic Kidney Disease - Everything You Need to Know to Help Your Cat. It has information about the different symptoms, treatments, where to get supplies cheaply. There's also information about food, like what to look for on the labels, what to avoid, etc.