I think there’s a slight confusion there.
The WebAudio sink will only send audio to any and all Web Browsers that have the PaperUI or HabPanel loaded. (I haven’t tried with BasicUI or Classic etc)
The topic you linked to moves on to talk about using Google Chromecast Audio dongles and seperate speakers in each zone.
Much as a Sonos / Heos / Yamaha audio sink might operate.
It would be amazing if there were a way to identify specific browser sessions and only send audio to that instance.
The big question is…
Do you want to play a music / audio file or would a TextToSpeech be suitable?
It is possible to push a TTS to specific instances of HabPanel.
Just setup a String item for each instance (or group of) HabPanels.
Then go to each instance of HabPanel and look for the Panel settings.
In there you’ll find an option box named “Speak the new value of following item when it changes”
Just set this to the String item you’ve assigned.
Then all you need to do is set the content of the String file in a rule / selection widget / buttons and so on.
As a laugh, I did use a https connection from my phone to OH and used a String item to capture SpeechToText from Google Android Chrome, then push that string.state into the Say commands in a rule, so that a unique announcement was sent to all audio sinks.
The idea was that we could TalkBack to the house, if we were alerted to something happening within the house.
I got it working well, and have not used it since.
(Other than surprising visitors)