How old is your boy? My boy came to a cat home as a puppy. He lays right next to Sugar, my female cat. My Male cat doesn't like him but he tolerates him. Petey doesn't bark or bother the cats at all. My parents dogs on the other hand go after the cats any chance they can get. But, I do think it's funny that if the cat doesn't back down, the yorkies are left standing there wondering "what do I do now, he didn't run away?"
Hopefully yours will at least tolerate them. Just don't let him chase and bark at them, he'll adjust eventually. Good luck.
Kimberly