Hopefully this will answer your question:
Here is my setup.
Scala Rider (Team Set)
Audiovox SMT 5600 Smart(cell)phone
The Zumo acts as the "nerve" center for the other 2 devices (cell and BT headset). AFAIK
, the Zumo (comparing to Nuvi, ect) is the only one that will let you conect a headset to it. At least compared to my little bit of research...
I can listen to MP3's being played from the Zumo to the Scala Rider and although it's just a (dual) mono output it works pretty well for music and phone conversations.
Better yet, I can use the phone book option (most BT cell phones will sync your phone book to the Zumo) or voice dial on the Zumo and it will control my cell phone which is in my backpack most often. If I am listening to MP3's and get a call then it will pause the playback and resume after I hang up.
I really like the Scala Rider apart from the voice prompts for nav and cell abilities because my wife likes to ride with me (as a passenger). Now, with the VOX control all one of use just initiates a conversation. Most of mine is "twisty ahead", "braking", "accelerating". I can say that it really makes her more comfortable just being in the "know" rather than the old hand signals and me looking back to her. I can keep my eyes on the road.
The Scala Rider fit my RF1000 Shoei helmet with no issue but my wifes Shoei (older RF800) was a PITA. I had to cut some of the leather on the side where it mounts and then stitch the ends (needle and thread) so it didn't rip any further. In the end, it was worth it.
Anyway, that is just my 2 cents.