Main L and R out connections are always on. There is no provision on Genos to toggle off the Main out signal.
The options "Headphones Switch", "On" and "Off" under Menu - Menu2 - Utility only apply to the GNS-MS01 Genos 2.1 speakers, but not the Main outs.
I use a mixer between the Main outs of Genos and the powered speakers, and use the respective faders / sliders on the mixer to control / silent the Main out signal of Genos to the speakers.
Thanks,
Paul