A:Answer Hello Dinhtruong, thank you for asking about this feature. It is a non-functional connection found on early production units and has been removed from the module. If you would like to connect a 2nd Acoustimass module to your system, 2 modules may be connected wirelessly to the SoundTouch 300 soundbar or the Lifestyle 600/650 home theater systems. Hope this helps! Have a great day, Suzanne – Bose Support