continuing on from the food thread for Candy; another thing to try - if they'll eat it that is - is 100% raw food for your cats. http://honeysrealcatfood.com/ is one of the supplies who provide the raw food with the necessary vitamins and minerals added to the food.
I tried it with mine and they didn't really like it, but then I also think I did the swap over too quicky and didn't do the slow gradual introduction of new food. But just a thought as this would be nearly 100% protein