Just to follow up on this I have done the DAB retrofit. It's not too difficult but fitting the tuner is really fiddly on a right hand drive car. You have to remove the throttle pedal to get it out and swap it.
To upgrade, you need a FM/DAB Tuner
1004787-02-D and Antenna Amplifier
1004798-00-D. The wiring for the DAB aerial is already in place, just tucked out of the way. Swap the tuner (under the dash on the right bulkead), replace the antenna amplifier (in the tailgate right hand side trim) and do a reboot. DAB will appear in the radio menu. You don't even have to do a firmware redeploy.