It is imperative to get a quality big that is at least 6'11". The Illinois game showed just how important it is to have size. Top level guards are the most important, but they need to have size to consistently compete in the Big 10 as well as the tournament.
The one thing Jirak could possibly do, is pull a big away from the basket since he can make shots outside of 3 feet. Manyawu never even looks to shoot it unless it is at the rim.