EDIT: was going to post a question — but realised there is a missing step in the the DK manual
Long story short, there is a missing step on Page 83 of the DK manual for getting the DT to play with the DK — it fails to mention that you have to set ‘TRANSPORT SEND’ to ‘ON’.
(which seems obvious now, but as someone who has never connected Elektron devices before, it seems like an important ommission)