Firehouse PA system

[iceman1575]

Some of the guys at the firehouse were talking about an in-house sound system for music/paging/radio traffic, etc. Just throwing ideas out there. Here's our current plan:

Radioshack 250w Amplifier (yes, cheap @ $89 on eBay)

Mic 1 - TV/Training Room Intercom mic

Mic 2 - Truck Bay Intercom mic (both for paging)

Mic 3 - New VHF Digital Radio audio input

Mic 4 - Old UHF Analog Radio audio input

CD - Music (either computer or radio)

The two buildings are separate. We're thinking about splitting the audio up, with the left channel powering the speakers (some cheap outdoor 5.25" speakers from PE) in the training/TV room/office, and the right channel powering speakers in the truck bay/gear room. Now, the only problem is, we don't want music talking over the radio traffic. Does anyone know of an interface we can hook in-line to the mic-1/4" inputs which, when a signal is detected, reduces the music volume in order to hear the radio traffic/page traffic? We're all going to be contributing to the system (I'll buy the amplifier myself, everyone else buys a set of speakers). What do you guys think? It's cheap & sounds complex, and it's not required, but it's a nice idea for us to have.