For years Sonos used to have custom apps for there speakers. ST at some point decided to make the methods, etc. Sonos was using the standard for music players. That’s why the Sonos apps worked with most other speakers. For voice notifications on speakers there used to be the Sonos ‘notify by sound’ app. A couple of months ago ST just pulled it from the marketplace and ‘replaced’ it with there own ‘Speaker companion’ app. I implemented the methods they require for voice notifications according to there documentation, but there new ‘replacment’ app just doesn’t recognize my DTH.
I did some testing and changed I believe the name and other stuff to Sonos and then I could select the speaker. However it just didn’t work. Since they don’t release there code I have no clue what to implement in order to work with their speaker companion.
If you’d like to install the old Sonos smartapps, they are still available on GitHub and as a template from the ST IDE. They let you create voice notifications on Cast devices, set the volume, etc.
So no need to buy Sonos speakers, just copy and paste the old source code into the IDE and you can install these apps again and voice notifications will work.