Will look at HK tonight or tomorrow. If they say you can add meat, fish, or egg though, I'd be uneasy. They have different protein and fat % and may not always be interchangable. It's a really good idea to talk to a nutritionist (preferably a veterinary nutritionist) about it.
Since they are completely asymptomatic, the % protein isn't a huge concern. You can stay between 18 and 22% as some experts seem to recommend, but really taking it a bit higher probably won't do a darn thing. Type of protein is important if you are concerned about diet, but them eating enough is more important than that...