Orijen is a good food and it is a results of slow cooking process over low temperature so actually this food similar to BARF diet in a way. I normally feed my Yorkies Orijen and Instinct of Nature's Variety. Once a while, I'll give them raw just to make the meal interesting.
For the aggression, if you make him wait then place a morsel of his food in his bowl. Give him an order to take it then add another morsel in his bowl and keep repeating this, it might help because he will make a connection that you are his source of food. If he growl at you, make a long pause before giving him the next morsel to show him that you are in charge.
About his diarrhea, I am not sure why. Some people said that you shouldn't mix kibbles with raw food but it didn't seem like you're doing it. Have you talked to his vet?
