...I know that ionbeam has used that feature of his street pilot along with his Bluetooth helmet headsets in the past...Something to do with the FM link and noise...
First came my Scala Q2s then I purchased a 2730. It quickly became clear how much turn-by-turn (TBT) voice instructions helped. I set my 2730 (hereafter GPS) on my computer desk and set it up to transmit FM instead of voice via speaker. Setting at my desk I put my helmet on and let the FM receiver in the Q2 find a FM frequency that was unused. I set the GPS to transmit at that same frequency. I told my GPS to simulate a ride and was thrilled to get the TBT instructions through my Q2. Next I loaded ~1,000 MP3s into the GPS and streamed music to my Q2. While the audio wasn't world class it was acceptable. I went on a walk-about in the house, GPS on my desk streaming away, helmet on and Q2 singing away. I had zero problems while walking around the main floor. Off to the second floor, where once again there were zero reception problems even though I was nearly 50 feet away. Cool beans!
The next day I headed out to Long Island. I had TBT out of my driveway and all the way until I hooked up with Fred W, then as we hit the road my TBT instructions went away. I couldn't get MP3s either. I fiddled with the phucker all the way to Sag Harbor with no luck. That night I redid the radio station selections with the Q2 and GPS. I ran around my room with my helmet on streaming all the way. The next morning when we left, almost immediately reception went away again. WTF?
I found several problems. The first and biggest problem is that here in the greater Boston/NYC area almost every radio frequency slot is used. If there is a free slot at my house, 20 miles away a radio station would be using that slot so the Q2 quit receiving. The Q2 must mount to the left side of the helmet and when I had the GPS mounted on the left handlebar reception was adequate until we got to an area where the formerly free frequency was now being used. At that point I had to find another free frequency and then later that frequency was used. I didn't play that game long. Then I moved my GPS to the right handlebar and discovered that the GPS transmitted directionally, and it was not directional from the right side bar to my left side Q2. The setup works very good inside because my aluminum sided house worked as a radio frequency shield, once outside without the shielding it didn't work so well. This past spring when at Mt. Tremblant Village, well away from any big city, the GPS and Q2 played nice again.
If a user lives away from congested radio traffic and mounts a 2730 on the left side handlebar or on the steering nut, the GPS/Q2 combo works. All other situations fail. I have given up on using the FM here in New England and use the 2730's speaker output to the headset in my helmet. I have the cradle for my GPS wired using the harness that wfooshee shows in his post. I used an extension cable to bring the audio out at the front of my seat where I plug in my helmet headset. I don't prefer this setup but it works quite well. Unfortunately, what doesn't work so well is when my wife is talking through the Q2's and Garmina is giving my TBT instructions at the same time :wacko:
https://www.fjrforum.com/forum//index.php?showuser=6354
And I'll even cut off the audio pigtail if you want for only 10 bucks more!!!! 
