Domes have only one LNB, it can be single or dual output but it is one LNB.
IF you have a SINGLE Dishentwork receiver, HD or not, the proper dome will work with it (NOTE PROPER DOME, not all do). But if you have multiple receivers you need 2 or 3 domes (3 max) and if you have more than 3 receivers a digital equipment switch to connect the receiver to the sat it needs to see.
With DirecTV, all domes save the tailgater work just fine, DUAL output LNB's will feed 2 or more (With switch) recievers. BUT NO DOME works with DirecHDTV. They use a different size antenna. (Different frequency band) and no dome currently made receives it.