Transitioning kitten to new food

I have a Persian kitten that is 11 weeks old and I could use some advice for getting him off Iams kitten and on to better food. I have 3 grown cats that eat Orijen dry and whatever grain free canned they are willing to eat. Ultimately I want the kitten to eat the same, but my efforts have resulted in diarrhea for the poor baby.  I tried giving small amounts of canned and mixing small amounts Orijen in with the Iams. This is what works for the adult cats. Didn't work for kitten. Fecal test came back negative for worms and parasites so I assume it is the food.

He isn't picky and clearly prefers the better food. If anybody has advice to help us make the transition easier I would be ever so grateful.

Unfortunately not all cats can handle Orijen. It gave my cat really bad runny stools. As a matter of fact, all dry food gives her the runs. Maybe kitty should just stick with wet food. Have you narrowed it down: does the dry, or wet give kitten the runs?

I would take kitten off the dry, and feed only wet to see if this makes a difference.