It's not the skin that's the issue, it's probably the kibble.
As for shampoo, try Johnson's Baby Shampoo [for real kids not the dog variety] OR try "OUT", which is a superior product [I've tried everything else too] and works to create a wonderful hand to the coat, is good smelling and is very inexpensive considering it's a top quality product. I get it at KMart locally.
I really recommend this stuff - it's worked on a show dog I had and a rescue dog I've got now. Both black coats gleamed like wet paint and the dog smells great for at least 2 weeks if you brush daily. <
http://www.outinternational.com/proddetl3.htm>
I'd give a new food a try too - and try adding some cod liver oil caps to your dog's feed. The bad coat dandruff is probably something he's eating and Canidae isn't the end all and be all of dog kibbles, you know?
Payton