The key to using the Amp100 with the Sonos is making sure you plug the Sonos unit into the RCA inputs for INPUT 2 on the Amp100. Before I realized this I was suffering shut off problems in quiet sections of music (as well as 3-5 second delays before sound could be heard in my speakers when I was first turning on the Sonos music).
The reason you go into input 2 is as follows: the way the Amp100 is designed, it sits idle with input 2 as the "default" active input. Input 1 serves as the "override" input, so once something is active on input 1, the unit switches to input 1. This is obviously set up this way so that the Amp100 knows what signal to give priority (Input 1) when two signals are competing at the same time.
Therefore, if you have your Sonos plugged into input 1 (whether or not you have anything plugged into input 2), there is a short delay when the Sonos comes on before the Amp100 realizes it needs to flip over to input 1. Similarly, if the song goes quiet, the Amp100 thinks input 1 has stopped and it reverts to its idle position in input 2. You end up hearing all sorts of clicking, and the music comes on and off during quiet sections as the Amp100 tries to determine where the signal is.
Drove me crazy for weeks!! Then I stumbled onto the issue/solution, after which the Amp100 worked exactly as I had hoped.
Plug your Sonos into input 2 and those delays and dropouts essentially disappear. The Amp100 is always ready and waiting for your Sonos signal on input 2.
Great amp for the $$ by the way.