Here's a link to a thread that talks about various foods, and I included some research into why there are concerns in a dry food only diet.Cat Foods
Any of these can be mixed with your Royal Canin. These are all described as premium foods, which stay away from by-products, dyes, fillers, etc. Each cat is different so you have to see what they will eat and which foods they will thrive on. In my personal opinion, a raw diet that is consistantly balanced with the necessary vitamins is the best food for companion animals.
Flint River Ranch