Penn is not a bad idea!
As for the food....diet is really the most important thing with a pup showing renal changes. I had a pup who had changes and she lived for many years after the initial diagnosis...she did not like the Hill's K/D and was on Purina EN for all of those years. Of course, if you are not happy with the RX diets, you could do a consult with a board certified vet nutritionist. You can find one at:
American College of Veterinary Nutrition There probably is one at Penn.