All I can tell you is that Hill's K/D and Purina N/F both work really well for renal failure. I have had more than one pup do amazingly well on those foods. I immediately saw changes in their BUN and Creatinine when they were on them.
As Brit said, renal failure is nothing to mess around with.
The only other option imho is a vet nutritionist and home cooking. You can find one at
American College of Veterinary Nutrition