I would probably go with a grain inclusive adult formula food, and see how he does on it. If he seems good after a couple of months, then stick with it. If he seems to not be doing as well as you'd like, then try a different formula.
Personally, I feed my two girls, a five year old American Pit Bull Terrier and an eight year old German Shepherd Dog, Pro Plan Sensitive Skin and Stomach Salmon and Rice formula.
In the past, I've fed Science Diet, Fromm, Bil-Jac, Nutrisource, 4Health, and a bunch of other stuff. For these two, the Pro Plan seems to be the best option.