I know this is an old post, but I just figured out how to connect Zumo, iPhone and second headset directly to first headset. My headsets are Moman O2E and specific commands to them are in italic.
• On iPhone set Siri to respond to "Hej Siri"
• Pair Moman with iPhone, DISCONNECT in iPhone
• On Zumo ...

I installed BT40 on my Goldwing. I modified supplied metal bracket. In high resolution the image s brilliant B&W 720p resolution. It is very useful in backing up. Also, I set up the side lines showing the width Goldwing needs on the sides and set the bottom yellow line to be 1 m from the back of the ...