He's a handsome guy! It's great you adopted a 6-yr. old. sometimes mature dogs are harder to place. once he adjusts to his new food, whatever you feed him, he'll be fine. I've always used Science Diet - it's a dense food that results in less poop, and mine like it just fine. Sherman's kennel used Diamond (I think that's what it was called ) , but he's adjusted just fine.
As far as changing his name, there's probably one he responds to more than the others - can you tell? does he prick his ears or furrow his head when you use a name? (personally I think he looks like an "Elmo")