I like to add raw eggs, cottage cheese, yogurt, oils and veggies. Every once in awhile they'll get table scraps but hey, who isn't guilty of this? I tried NuVet for awhile(supplement)...wasn't that impressed. I'm gonna try Vertex suppliments during training time this spring/summer.
Alot of people will tell you that you only need to feed a high quality diet in order to get a balanced meal. I think it really depends on how active your dog is. Nutro Max isn't a high rated food but decent I suppose. Here's an old link to grading your kibble...hope this helps. Dog Food Analysis - Reviews of kibble