You need a preamp capable of routing simultaneous inputs to multiple outputs (AKA a matrix switcher), a multi-channel amplifier, and a way to control the gear from the remote locations. You can build your own, or purchase a pre packaged soultion. All in one box products, basically multi-zone receivers, are available from AudioAccess and B&K. Elan, Xantech, Audio Control, ADA, Intellinet, Niles, Sonance, Russound, Linn and a host of others offer packaged (some assembly required) solutions at varying price points. DIY sources number in the hundreds, there is a fair amount of computer related hardware that can be used for this purpose. There is an organization of professional installers, CEDIA, that can help you if you lose your way.