In our black box theater, which is used as a classroom, the school failed to include speakers for the school Public Address system, which also includes bells between classes. The solution that someone before my time came up with was to run a line to the audio rack, and run it through the audio system in the theater. However, this means the amps have to be powered up any time school is in session. This seems wasteful to me both in terms of power consumption, and the life of our components. What I'm wondering is, if there is a way to add a small, low-power always-on amp to the system, and route it through the speakers, and then have some sort of relay that switches between the school audio and the theater audio automatically when the theater sound system is powered up. Is this a reasonable way to do this, or am I just better off adding a separate set of speakers and amp just for the school feed and putting a kill switch on it up in the booth?