I would like to know more about how you plan to connect this electrically. Do you plan to try to feed the audio out into your VOICE II intercom?
I have an 07 with Nav III also and am contemplating my options. I can still load maps into my III, but can load only a few states due to the limited memory. I'd rather not pay the toll for the BMW brand, but I dont want yo trash my wired headsets that work with the VOICE II.
I went ahead and bit the bullet on a Garmin 590LM, as I could not get the map updates to load onto my Nav III. I have a Scala G9 bluetooth comm system, so I plan to use it linked to the GPS, and have never really liked trying to listen to the LT's radio or CD, except when parked. My preference would have been to have the new GPS operate similar to the Nav III through taping into existing wiring harnesses, but since I'm somewhat electrically challenged and was unable to locate any wiring schematics showing the radio/com systems, decided to mount it in the same location while using the old Nav III stingray bracket.
The 590 cradle does have additional wiring for a USB power outlet (to charge a phone or other device), as well as three connectors for mic in, audio in, and audio out. You should be able to listen to Pandora radio through a smartphone, linked via bluetooth and then routed from the audio out cable to a wired headset.
In the brief time I have had the new GPS, I've connected and played an i-Pod through my helmet speakers, but have not taken it out on the road yet, as I am in process of installing Spiegler brake lines and have the tupperware off. Here's three pix of the cradle mounted on the bike, the 590 mounted on the cradle, and the three connectors that I will leave under the seat, unused most of the time. Power is picked up from my Centech AP-2 fuse panel. I hope this helps in coming up with a solution to meet your needs.