I have just begun dabbling in the esoterica of multiple pairing of hands free sevices and my Sena SMH10 headset now that I finally have my Zumo 590 GPS installed on my Spyder. Here is a capability statement from the SMH10 user's guide.
"Typical Bluetooth headsets can connect with only one HFP (Hands-
Free Profile) device, but multipoint pairing allows the headset to
connect with two HFP devices at the same time. So, when you already
have a mobile phone connected with the SMH10, you can also pair
and connect a second mobile phone or other HFP devices such as
GPS or Sena SR10, Bluetooth adapter."
Before I got the GPS I had my iPhone and the Sena SM10 Bluetooth transmitter paired to my headset. That way I could listen to the Spyder radio(s) and my phone through my headset. Now, my GPS and phone are paired to the headset but I do not have pairing with the SM10 because of the two HFP limitation. To get music to my coconut I downloaded a bunch of CDs to my phone, connect it to power in the trunk and manually turn on the phone music. More dabbling to do on this. Sorry, I don't know squat about the 20S headset. Good luck!