You select what speakers you want powered via how you set them up inside the setup menu. Your not going to blow the amp up unless your speakers are 4-ohm.
You can have either the surround or heights depending on what you chose to play. Personally I'll run the heights vs the rears, that's how I have mine setup, plus I don't have the room or rears right now. Once I move into a bigger place than I will have the rears powered as well.