Just finishing a new building we went through this. The electrician actually was trying to wire in the system when i stumbled upon him. I politely told him to get out of my rack. As you have heard it's best if your system allows it to do a low voltage signal to your dsp to temporarily mute the system. This requirement was thrown in at the last minute by our Fire inspector. The room was to be exempt from this requirement but we ended up getting the greenhorn inspector that came up with all sorts of stuff we had to do. To appease the inspector we did a remote mute through our dsp since it just so happen to be capable of it.
In venues that fall into the requirement of needing this i have had to do other tricks as well. One inspector wanted instant off and with capacitors in the amps they were taking a few seconds to go out. We ended up having to put in relays for all of the loudspeaker wiring in that project just for a few measly seconds.
Lots of ways to accomplish this code meeting application just be aware that some inspectors have a different way of viewing things.