I don't use MP3. I prefer to listen to the radio. MP3's don't give you traffic reports.

It would be nice if the audio system would allow for an AUX priority so you can receive the GPS instruction. I don't have Bluetooth either.

 

I have the HD radio and Zumo 550.

I am using the helmet headset for bluetooth calls. There is a special (low cost) interface that allows you to plug into the 2.5mm jack on the Zumo bike mount (located above the Zumo audio out 3.5mm jack) and allows you to use your helmet headset for both CB and bluetooth.

Simple, clean, inexpensive and crystal clear calls at 70mph!