Originally Posted by Nigel Goodwin:
“Why would a soundbar have an HDMI socket on it?.
They generally have optical in, and two phono's in.”
My Panasonic sound-bar has HDMI in & out, and it links directly to the Panasonic TV's audio controls. If the sound bar is switched off audio is routed through the TV speakers and when adjusting the volume the on-screen volume display label shows 'TV Volume'. Switch the SB on and the label changes to 'Home Cinema Volume'. The SB also toggles the LED on it from green to orange for TV / DVD viewing.
In answer to the OP though, the TV remote control adjusts the SB volume as the signal for it is sent from the TV. This is for Panasonic kit though linked through HDMI-CEC, which Panny refer to as Viera Link..