Thanks for asking, you may be right.
It turns out it is just the slightly confusing set up options.
I got it to work thus:
Audio Hardware = Map output for decklink.
BUT
Playback Audio device = NOT Blackmagic Playback but Adobe Desktop Audio.
maybe it is a decklink driver issue after all
Am not entirely sure now which I am listening to, so if it is out of sync then meh!
Nobody cares anyway.
