I plugged a headset into my Beosystem 3, but the external speakers didn't become mute. I couln't find an adjustment in the Beosystem 3 menu. Anybody having an idea ? Thank you !

Hi~~ I'm assuming the BS3 works the same was as the Avant.  Plug in the headphones, then on the Beo4 remote, press right in the middle of the volume up/volume down button on the lower end of the remote.  This will turn off sound to your speakers and only send sound thru your headphones.  See if that does the trick~~

Thanks beobres ! That really helped ! :)

Glad that helped.  I remember being confused trying to do the same thing when I got my Avant years ago.  My BS3 is being installed June 11 with the rest of a new B&O home theater set-up-- so I'm jealous you already have yours~~