It would be really helpful to have a slider (instead of just buttons) to adjust the master volume of a group of zones. This would greatly enhance the spousal acceptance & usage factor.
Replying to an old thread because I agree
We need a master volume slider to control all grouped zones.
I am using multiple Sonos devices to play music casually throughout the main floor of my house and it takes too long to adjust volume for each individual device.
It seems there is tons of room for the slider to be implemented in the area I have indicated.