Well the best way to think of it is that watching a live tv channel is one event, and recording a tv channel is another event. Bearing in mind, all Hoppers can record all main local stations (Fox, NBC, CBS, ABC) at the same time and it only takes 1 event.
So that said the breakdown is like this...
Hopper Duo = two events maximum
Hopper or Hopper w/Sling = three events maximum
Hopper or Hopper w/Sling + Super Joey = five events maximum
Hopper 3 = sixteen events maximum
Hope this helps to answer your question!