Many home theater receivers have built-in multizone and multi-source features. Multisource operation is important because each zone can select a different source - for example, FM radio in the kitchen, CD in the den and iTunes music in the bedroom.
Some receivers have built-in amps for stereo music (and sometimes video) in as many as three separate zones or rooms, even the patio. Just run speaker wires to other rooms and add speakers. In other models the audio output is line level (unamplified signal), which requires a stereo line level cable to each zone, an amplifier (or receiver) and two speakers in each room.
Some home theater receivers allow reassignment of the surround channels to power speakers in another zone. For example, some 7.1-channel receivers permit the two surround back channels to be used to power Zone 2 speakers with independent source selection. The main theater room has 5.1-channels and another room uses the two surround back channels.Sources connected to the receiver can be controlled from each zone via a wired remote control connection or with a remote control extender.
These AV receivers from Yamaha, Denon, Onkyo ,and Pioneer are a few examples of the multiroom receivers available. Read more about multiroom av receivers from Robert Silva, About.com guide to Home Theater.