Plugin for logged-in user to see different Theme than a visitor?

I am developing a WordPress site that needs to have a very different theme shown whether the user is a logged in user or not. For example, if they are a visitor, they see Theme A, but if they are logged in, they see Theme B. I looked at the Test Drive plugin, but that does not fit my needs because it is a temporary solution. Are there any other suggestions for ways to make this work?