Dave Meikle came up with the excellent idea of using an inexpensive FM transmitter plugged into my Harley radio and then simply listen to the radio via the Sena's FM radio feature.  These FM transmitters are commonly used to make an MP3 device play from a car's FM radio sound system.  They work very well for that.  But Dave's idea to use an FM transmitter to interface with our Sena 20S headsets is just what we needed!  I attached a picture of it on my tank console. 

I'm here to report that it works magnificently!  AND, it opens up so many more new possibilities.   I've been sitting on the motor down in my workshop for the past 2 hours trying every possibility that I can imagine.  They all work.   With this configuration, the Sena/Zumo/HD Radio/iPhone do so much I need to explain the possibilities.  I have a 2013 Harley Limited with factory AM/FM/WX/CB radio so I'll use my experience as an example.  This will actually work with any factory radio or other receiving device that has an earbud jack audio outlet. 

1.  Listen to the Harley radio:  I used a Harley console connector to mini audio female adapter, the kind that one would use to ride with earbuds connected to the factory radio.  I purchased a cheap FM transmitter from New Egg. 

(http://www.neweggbusiness.com/Product/Product.aspx?Item=9SIV04S20W4853)

This is the harley adapter:  http://www.spoiledbiker.com/harleyadap.html  

Today, I plugged it into the Harley via the mini phono adapter and set it to 99.1 MHZ (could have been ANY frequency).  Turned on the HD radio to an AM station.  Told the Sena lady, "FM RADIO".  Tuned the Sena FM to 99.1.   Suddenly, I could hear the AM radio in my Sena headset helmet clear as a bell.  Tuned the HD radio to an FM station.   That worked, too (although I could have just as easily tuned the Sena to a different commercial FM station.  WX radio, Yep.  CB?  I could hear truckers talking.   It works.  Harley sells a separate hand microphone if I really want to talk CB.  It'll plug right into one of the adapter's ports.  

2.  Using the Zumo via the FM transmitter:  Next step was to listen to the Zumo's MP3 player via the FM transmitter to my Sena 20S.  I told the Zumo to forget the Sena 20S bluetooth device so that the Zumo and Sena are no longer directly connected.  Instead, I have my Zumo output plugged into my Harley radio's AUX jack.  so when I switched the Harley to AUX, I heard my MP3 music in beautiful, crystal clear, hi-fidelity stereo!  Wow, this works great.   

Next with the Zumo was driving directions.  I set a destination in the Zumo and it stopped the MP3 music and gave me navigation directions.  When the Zumo lady was finished, the MP3 came back.   I also did this with XM radio playing listening via my Sena's FM receiver.  Super!

NOTE:  With the Zumo not being paired to the Sena as 1st phone A2DP, the Zumo audio is being received by the 20S FM radio feature via the Harley radio AUX and the FM transmitter.  The navigation directions, alerts, beeps, etc. DO NOT blank out the Intercom.    This is perfect!

3.  Phone usage:  This is where it gets a little tricky; but well worth the effort.  I have my iPhone paired to the Zumo.  I also have my iPhone paired to the Sena 20S.  All the phone features of the Sena work as the User's Guide explain with this method.  

Receiving a phone call:  When the phone rings, I see the caller's name on the Zumo.  But the phone must be answered by the Sena because there's no microphone connection to the Zumo from the Sena; the calling party will not be able to hear me if I answer via the Zumo.  BUT,  the iPhone is also paired to the Sena.  If I want to answer the phone, I simply push the phone Sena phone button one time.  It answers the phone and we can talk.  The Zumo doesn't know that I've picked up the phone via the Sena.  To end the phone conversation, press the Sena Phone button again and phone call will be ended.  

Making a phone call:  I can initiate a phone call via the Zumo's interface.  Using the Zumo, I can see my iPhone's phone book and can select the person to be called.  (or select from call history, of course).   Once I've selected the person to call, I initiate the call from the Zumo; and then press the Sena's phone button to be able to talk and listen.   Ending the phone call should be done by ending it on the Zumo (and maybe the Sena as well).    

Then, I discovered something new:  I can use the iPHone Siri lady to make phone calls or get information on anything I wish while riding.  I pressed the phone button once and the iPhone Siri lady asked what I need.  I said, "Call George".  She confirmed which George in my iPhone to call and made the call after I said yes.   Now, that's pretty cool.  Voice dialing to people in my iPhone phonebook via the Sena!

Four of us with Zumos and Senas are embarking on another 5,000 mile motorcycle camping trip next weekend.  We're expecting a much more pleasant Sena  20S experience.  Not only has Sena fixed  some of the bugs that they had in the first run and now have the Group Connect working well the Zumo Lady will no longer be interrupting our intercom conversations.  We will be able to communicate while the Zumo is directing us to our destination via the FM radio instead of blanking out our important conversation about where to turn, etc. when we need it the most.  

Gosh, I think that's all.  I'll update if I learn anything new.

Ken