Since you are using GAR, that means you have an RPi running correct? By chance, are you running Node Red on that because there is a palette, node node-red-contrib-cast, that does what you want and it's fast and it says exactly what you type, no prefix with "broadcast by Bob...."
You can also send it URLs to audio/mp3 files. Mine has Darth say "I am your father" when I am almost home.
