I got it sorted out. I reset the Boom audio system back to factory defaults, then re-paired the rider headset. I didn't need to configure anything within the menu system initially as it defaulted to what I needed once I plugged my phone into the USB port - it started Apple CarPlay and my music began to play through the bike's speakers and the left thumb toggle operated the volume just fine. I tested the phone (through CarPlay) and found it was routing the incoming audio through the bike speakers so I went into the Audio Menu, and chose to have phone calls sent to the headset icon - solved that; the left thumb toggle operated the volume during a call as it should. I tested texting (through CarPlay) and found that Siri (or whoever she is) was reading the texts to me through the bike's speakers so I again went into the Audio Menu and chose to have Prompts sent to the headset icon - solved that. I had to go into the volume menu to boost the Prompts volume. The right toggle switch works as I believe it should to cursor around in CarPlay to the various 'clickable' buttons - you press the toggle in to activate the button.

Once I got the Rider headset working properly, I unplugged the phone and then paired the passenger headset. I then went into the main menu and made sure that both headsets had INTERCOM 'Enabled' and I then went to the volumes menu and found the intercom volume and turned it up. To actually turn the intercom on and use it, you have to be on the Boom screen (not CarPlay) and click the headset icon at bottom center - it will bring up a dialogue box for the intercom and at the top right of the screen there is an on/off button for it.

I hope I remembered all of this correctly.