It is annoying to manually control my subwoofer, which is located at the other end of the living room. To avoid this, you must implement your own "master / slave" circuit. First step is to detect when the receiver is turned on or off in a secure manner.
I can't get this information via the receivers buildin network interface . It works only if the receivers is switched on.
A much more elegant way is a load depenting relay. I choosed the Eltako AR12DX-230V relais. The advantage is that it does not turn the receiver in standby but really only when a set load limit is exceeded. This relais is connected with an universal interface which sends the current state to openHAB.
The socket of the subwoofer itself is controlled by a switch actuators.
An additonal openHAB rule translates this states into on/off switch commands for the subwoofer socket.