I have the maps on a SD Card, so I went to garmin site and installed free voice straing to the device via their browser plugin[Please Register or Login to download file]
clicked Install Voice Directly To Device
and there was a folder called Voice under GARMIN and a file called Squirrely.vpm
When I put the card in the Kenwood device, I can't see the option of choosing voice and hence I think the device is not compatible to add extra voice.
Thanks a lot for your post