If nothing seems to help use Mute key on Keyboard

Yes, I nearly went crazy using my Windows PC streaming to my Raumfeld Connector2.
Because everytime I played a song the sound was doubled with delay. But switching it off via mouse or touchpad in windows loudness bar everything was muted at all.
Unexpected Solution was to mute on hardware keyboard by pressing this “Mute”-key with a crossed speaker symbol on it…

May be better updated at the faq page?

this did not work for me- mutes everything like turning the pc speaker volume down.
anyone else have a solution?