I had the same issue with Hans on Orijen - almost instant diarrhea, and I was feeding him 1/4 of a cup of Orijen + 3/4 cup R/C, so not overdoing it.
I also tried Go! ALS but he didn't like the taste of the kibble.
I may try Acana or Wellness when he's older, done with experimenting for a while. I have to say that I've tried the Wellness canned food and he's done really well on it, as well as the Merrick grain free canned.
Rough Collies - King (01/1994-01/2002) and Samson (2/14/2002-3/30/2014) - too good for this world
GSD - Hans (12/31/2013)