Problems with Innova EVO

For the last week I have been trying to transition from Eukanuba Natural Lamb to Innova. I bought two 6 pound bags, one regular Innova and one Innova EVO and mixed them together. Each day I would feed a mixture of half Eukanuba and half of the Innova mix. Freckles seems to be doing fine but Duke started having constipation problems. It seemed to be getting worse so I put him back on Eukanuba.
The EVO is very high in protein so that may not agree with Duke's system. Freckles, on the other hand can eat tennis balls without a problem.
Is anyone here feeding Innova EVO? It is touted to be the BARF equilavent in a kibble form.

 

innova is an extremely rich food, an so different than the Eukanuba. I think mixing half up front is too much, I would start by using a 1/4 mix not half with the Eukanuba and see if that helps