Independent volume control while in Group

[sabinlazar]

Independent volume control while in Group

[ebaauw]

My setup is comprised of 4 Sonos Play1 speakers and 4 Philips Motion Sensors.

That resembles my setup: multiple rooms with Sonos players and Hue Motion sensors and lights. When I enter a room, the lights turn on (when it's dark) and the music starts playing. When I leave the room, the lights and music turn off.

I created automation rules inside Apple home app and using the Hue Room lights for triggers

You might want to check out my homebridge plugin for the Philips Hue: it exposes the Hue motion sensors to HomeKit, so you don't have to use a light as trigger (and the lights can remain off when there's enough natural light).

I use this approach of turning the volume to 15% for on and to 0% for off...

You might want to use Mute instead. It's less confusing, as the group only goes on mute when all member zones are muted.
I actually use the Speakers Power (on/off) characteristic in my HomeKit automations, to have the Sonos join/leave the group instead of adjusting the volume.

...to get rid of the delay existing when using the on/off (play/pause) speaker setup.

Do you mean the delay in the Sonos connecting to (and buffering) the audio source? That's probably less of an issue when you make the zone join the group of another zone already playing the radio station.

by controlling each zone independently, the speakers audio source is not synchronised

As far as I know, grouping zones is the only way to have music synchronised across multiple zones.

but when I try to automate it or control the volume of the individual speaker from Home app it affects the group volume

Yes, that's how Sonos works: the group volume is like the average of the volumes of the member zones. The volume of the other member zones shouldn't change, though, when adjusting the volume of a single member zone. You see the same behaviour in the Sonos app: when adjusting the volume of a single zone in a group, the group volume changes as well, but the other zones remain unchanged.

Is this desired scenario possible?

Yes.

Am I missing something?

Please note that the Volume (and Mute) of the Sonos services are linked to the group volume and mute; the Volume (and Mute) of the Speakers services are linked to the individual zones.
So when you set the Speakers volume of one member zone, the Sonos volume of all group member zones changes, but the Speakers volume of the other group member zones is unchanged.
When you set the Sonos volume of one member zone, the Sonos volume of the other member zones changes (because these all point to the same group volume) and the Speakers volume of all member zones changes (because of the change to the group volume).
It's confusing, I know. Best ignore the Sonos service Volume and only look at the Speakers service Volume.

[sabinlazar]

Thank you very much Erik for the detailed explanations and suggestions! I use the Speakers service and mute instead of Sonos services and everything works as expected now.

Many, many thanks!