If you are not using the Sonos Amp in conjunction with a TV via the HDMI_ARC port; but instead to power your favorite speakers, you'll still want to avoid the hassle of getting up from your listening position to adjust volume.
I found the Logitech Harmony 665 Universal Remote to be the perfect companion. It allows me to adjust volume up/down and mute. Programing it works with Windows and MacOSX. After you download/install the UI software; and set it up using your computer, just follow the instructions in the Sonos App to make it work with the Sonos Amp.
Here's a link; but it can be purchased for less elsewhere...like BestBuy. https://www.logitech.com/en-us/product/harmony-universal-remote-665?crid=60
Enjoy your Sonos Amp. Cheers!