Using a Shelly or Sonoff to trigger a 12v sensor on a music amp

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I have a few Sonos Connects connected to a 16 channel amplifier. The amp can be turned on manually, by a 12v trigger, or through music sensing (ie., it detects that one or more of the Sonos’ is providing it with a source input and it automatically turns on the amplification).

I don’t have a 12v trigger, so I rely on music sensing to turn the amp on and off. This works OK at loud volumes when it is easy for the amp to sense the source input, but the amp often can’t detect the music source when the source is set at a low volume. This will cause the amp to turn off during the middle of playing music at low volume.

I’m thinking about using a Shelly 1 or a Sonoff LV to either supply 12v to the trigger or as a smart relay switch to the amp directly. In either case, I’d set up an HA automation that would trigger on one or more of my sonos changing state from “pause” to “playing”.

I’m pretty new to HA (although I am comfortable with writing automations/templates/etc.), and I’ve never worked with with either the Shelly or the Sonoff. I’m guessing that everything will be easier with the Shelly as I can rely on its native MQTT implementation.

Does anyone have any advice, warnings or corrections about my plan? It seems pretty straightforward, but I’ve fooled myself into believing that about other rats’ nests before.

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I know this was an old post, but I’m doing similar research. I used an iTach by Global Cache to send a variety of IR commands out of a flasher to a few devices in my AV Cabinet, so naturally this gave me the ability to turn on my receiver and set the input, so I used the first part of your idea (sonos play state change as trigger) and then sent the IR command for those instructions.