Suppose I have 5 Macs sharing their libraries. Suppose I have 3 Airport Express units per Mac. Suppose that gives me 15 distinct audio zones (AirTunes can stream music to three different Airport Express units). If I was using that set-up in new home construction, what would be the best way to get the audio into some ceiling speakers? The Airport Express has an audio out port, but I'd need powered speakers in the ceiling.