I’m assuming the Amp is grouped with the Arc, not powering rear surround speakers? If that’s the case, just tap the dot on the volume control and it’ll show independent controls for each “room.”

early rejector - I am not sure what you mean by grouped with ARC. How else could I be using it? It must be hooked up to something. I set it up to power rear speakers but I want those to be playing without the ARC in a certain instance. I am looking to turn the volume down on the ARC or up on the AMP.

When set up as surround speakers, there is certainly an ‘extra’ volume control in the room settings under ‘surrounds’. In the same place where you set ‘ambient’ or ‘full’ when playing music, not the TV input. However, you can’t ‘mute’ the Arc completely, just turn up the surrounds, relative to the volume on the entire ‘room’. 

There’s two ways of setting up your system. As a surround set up, whereby the Amp is in the same Sonos “room”, or as two different rooms, whereby you have two “rooms” that you would “group” to have them play the same source. Question is: do you use your Sonos system in the former or latter type.