https://www.sonos.com/en-us/shop/port

The12V trigger automatically turns your amplifier on so you can just press play in the app. No extra remote required.

There are also many  amps and receivers that will automatically go from standby to playing an audio source when it sense audio on the inputs without the use of 12V.  I use one with my Port.  Not relevant to your case, but all Sonos products with inputs have this capability as well.

Thanks Danny.  Unfortunately, the receiver I'm using does not have input-switched standby mode.  I was considering trying out a solid state switch that would work with the 12VDC Port switching signal, just require a little wiring on my end.  Not sure if it is worth the effort, maybe I just need a different receiver...

What I would do. I don’t know about the US, but EU mandates the auto standby mode that has very low power consumption, and the signal sensing feature that automatically turns the receiver on when the signal is sensed at the line in jacks is usually also a part of that mode.

@Pumpkinking save yourself the hassle and buy a little peace of mind: On amazon.com you can find an AC outlet trigger box for $30, with a trigger voltage anywhere between 3.3-60VDC & 12-120V AC!!!  It even has 2 NO and 2 NC outlets, i.e. trigger for either on or off!  The only limitation you might care about is 12A max @120V, on a thermal circuit breaker.  (It doesn’t have a UL listing, but 20 years ago I wired my own, to match up with B&O “PowerLink” speaker trigger and mine sure as heck wouldn’t have passed!  Nowadays, just don’t bother DIY.)  Search for “IoT Relay”, or its product ASIN, which is B00WV7GMA2.  (No affiliation and no experience either, but the manufacturer Q&A looks good -- about to order one myself right now, just to test it out.)