Thanks - yes, I have MIDI To set to digitakt. And I have 16 channels.
If I have it set to 1-8, I can ‘play’ the main samples. But if it’s set to 9-16 (i.e MIDI tracks), nothing happens.
Yet if I press, say, Track 9 on the Digitakt, it triggers the Synth as you’d expect. It’s definitely not Muted on the Digitakt for example.