When both rider and passenger have their headsets bluetooth to the boom radio how is rider to passenger communication achieved, is it via the boom radio or is it through the headsets (as if they were not connected to the boom radio)?
It is through the boom by default. If the passenger wants different music, don't link it to the boom just their phone. Then you can link the two headsets to each other directly.
When both rider and passenger have their headsets bluetooth to the boom radio how is rider to passenger communication achieved, is it via the boom radio or is it through the headsets (as if they were not connected to the boom radio)?
Either, we have found it best to shut down the Boom function rider/passenger and use headset. Of course your needs may very.
In the head set setting having the back round music disabled not keep playing in the back also works better for us.
In setting for head set you will see Intercom-Audio Overlay Sensitivity You can choose between 6 levels or disable it.
You may wish to adjust some of the setting to fit your needs.