brimforge said:

Sidious is the "real" master of Dooku and gives orders to him offscreen, we only see Tyrannus in what were scenes with Sidious

Yeah, that is what I'm going to do, I've always had a soft spot for the 'rule of 2' in the prequels, it makes the sith seem more sophisticated and gives them history, it shows that there are only two because if there are more then the master will be assassinated. That is why I want Dooku to be looking for secret apprentices behind Sidious' back [sort of like the force unleashed for you gamers out there ;-)]