You could attach each of your AppleTV's or airport expresses to one of these tiny inexpensive stereo amps. They are small digital amps but they only accept analog inputs, but your ears are analog too. So, you have to go analog sometime. Unfortunately, they do not look very stackable. With all these amps fired up, you could control library sourcing, music choice and volume for all six zones from your iPhone's Remote application.
7/7/10 at 12:48pm