For the nuvi's there all made to work with phones but not headsets. The only one's that can pick up the headsets and generall work will be the Zumo range as they have 2 different profiles. One for phone and then the other for headset / helmet.
Think you will find the Bluetooth will only connect with a phone to allow the GPS to act as an handsfree unit.
Couple of things you can do for a Bluetooth connection.
If you have a 3.5mm earphone socket you can get a Bluetooth transmitter cheaply from Ebay that will allow you to listen on a Bluetooth headset.
Better yet get something like the Nokia 5230 for around £100 or less, it has GPS navigation, and can pair with Bluetooth headsets. Brilliant phone that can play movies, browse the internet, play MP3, and has GPS navigation.