Chess AI really isn't that advanced at all. Chess is not a solved game, so for beginning part (the first 15-25 moves) computers are actually very poor. They compensate by selecting moves from a database of human games pruned by humans for computer use. It's more like a scripted response than AI. However as the game simplifies and becomes more of a tactical question than a strategic one computers are in their own league.
To prepare for the tournament the players will look over a database of chess games selecting what they feel is relevant for their oppent and then manually search for new moves/ideas in those positions. Computers make sure there are no tactical errors and double check the players work.