Yamaha NS-P400 Owner's Manual page 10

If your amplifier has only one set of main speaker output terminals
Connect the speaker output terminals of the amplifier to the INPUT1 terminals of the subwoofer, and connect the OUTPUT terminals
of the subwoofer to the main speakers.
Subwoofer
To AC outlet
10
Main speaker
Right
OUTPUT INPUT2 AUTO
TO SPEAKERS POWER
ON OFF
FROM AMPLIFIER
INPUT1
Main speaker
Left
OUTPUT INPUT2 AUTO
POWER
TO SPEAKERS
ON OFF
FROM AMPLIFIER
INPUT1
Amplifier