There are many products out on the market at the moment that allow you to listen to audio in different rooms from a single system.
The best and easiest use networking, either wired or wireless, to communicate and usually require a central server to hold music files.
One of the best systems is Sonos which uses either wireless or wired networking to communicate between units. The system can be controlled by the Sonos proprietary controller, iPhone, PC or Mac and can distribute audio from a central server, internet streaming radio or standard hi-fi equipment such as a CD player.
