Help with Underweight Husky?

My husky is 3.5 years old, 24.5 inches at the shoulder, and weighs about 30 pounds. You can feel every rib and see his vertebrae. When he went in about 8 months ago to be neutered he weighed 46 pounds. My vet ured me that while he was under-weight, he is in great health and that it is common for huskies to have low appetites and high metabolisms, and being that he is an ex-sled dog, this is probably magnified. He is clean for internal and external parasites. He is a very finicky eater, currently eating about 3-4 cups of Actrium a day, (not the best quality but it is what he will eat) and despite our best efforts will not eat any more then that amount of kibble food. Wet food seems to give him diarrhea, so I would like to stay away from that as much as possible. If any one has any advice to offer, I would greatly appreciate it.