Add attribute to speaker group?

Hi,

I can’t find how to add an attribute to my Sonos speaker group.
I have 3 Sonos speakers which I’ve grouped to a speakergroup with the help of “helpers”.

Now when I add a single Sonos speaker to a media card it shows me a picture of what it is playing. When I add the speakergroup to a card it’s now displaying that currently playing picture.

Now I’ve pulled the following attribute from the ‘single’ speaker.

entity_picture: >-
** /api/media_player_proxy/media_player.sonos_era_keuken?token=xxx**

How can I add this attribute to the speaker group entity? I can add it through the Developer tools obviiously but that dissapears after a refresh/few minutes.

Help is greatly appreciated :slight_smile: