What makes you think they are going to change anything? All of these guys coached 3-5-3 at Montana. I can only go by what I have heard from BB. And some of it is BS. But unless you have Buddy Ryan and 13 defensive players the Bears had - for any defense to be successful what they do has to fit into an overall game plan.
Since i have already commented on this more than once, the Illinois offense is quick strike, fast pace approach which leaves the defense on the field for more than 30 mins/game.
Therefore the "best fit" defense is one that (1) doesn't give up big plays and (2) finishes on 3rd and long. With the returning players we have, that would be the correct strategy regardless of formation. Its all about personnel an match ups.
Now I don't think it takes a rocket scientist to see BBs frustration. The defensive mechanics that Hauk was using (firing linebackers and leaving corners in man cover) is designed to make the big play. But when it doesn't make the big play, it gives up large yardage.
BB wants his defensive backfield to be the strength and by isolating them so often, bigger or more athletic receivers are going to be able to get the ball. And we certainly saw enough of that on Saturday.