I Do know that Innova is really highly digestable grain, that is why the stool is i guess compact and not so much? (although mine poop about 3-4 a day)..
And I guess the other reason why you are able to see the grain with the Merrick is because the grain isnt as digestable as the Innova.
If you'd like to do your own research, my friend is doing a dogfood project and has done tons of research on dog food, and she recommends Innova EVO.
www.mordanna.com/dogfood
or you could always go on Innova's website and get a hold of them for any questions you might have.
www.naturapet.com
I hope that helps!