Sorry Dave - I misunderstood your requirement. You just need a cheap BT receiver! Plenty on Ebay and Amazon, I'm sure. They will all have 3.5mm socket outputs which will fit all stereo earbuds, or slim pad speakers for inside your lid.
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If you are looking at progressing to bike-bike comms then the Sena is supposed to be the "daddy" just now, because it is reported to pair up with the other makers' units.
A group of us (2 at first, becoming 3 and 4) went for the Scala G4, and found it to be great, but things move on, and the ability to have open comms between 4 or more bikes might be an advantage.
To be honest - I use coily-cable to hook in my iPod to my Scala, and seldom use the bluetooth from the satnav as I've only found the spoken directions to be desirable in the heaviest of city traffic, and even then - I still steal a glance at the screen.
Everyone is different, however.
The 660 is a great unit, but must be nearing end of production soon? You should be able to get one for around £310 with lifetime mapping?
I bought a little 220 for use on my sporty-bikes, but for sure the 660 is better for displaying more information on the screen (for touring mostly - Arrival at Ferry, miles to turn, miles to go - etc)
Have a look at the 340/350/390 too.
Al