Sena suggested that I pair the Zumo as an audio device, and the iPhone as the 1st phone. That makes the iPhone the A2Dp pairing and the Zumo operate as HFP. Not good, since I listen to stereo music and MP3 via the Zumo. This is to keep the Zumo from being 1st priority when paired as a phone. (which is horrible).
OK. but now, each time I turn the Sena ON, it has forgotten that it's paired to the Zumo. I have to re-pair the two together. That wouldn't be so bad, except it's taking 20 or more tries before it finally says "successful".
The process includes holding the jog button for 6 seconds; or until the Sena lady says "Intercom Pairing". Then, you have 2 seconds in which to press the phone button. I finally had to take the helmet off my head to see the light. Then, the next 20 or so attempts to pair with the Zumo were fails. Suddenly, it paired (and I did nothing different).
As a test, I turned the Sena and the Zumo OFF. Turn them back on: The Zumo thinks it's still paired. The Sena doesn't seem to recognize that it was paired to the Zumo. So back to 20 some-odd attempts to re-pair it again.