I was also looking for a simple solution, but unfortunately there isn’t one, as Engine ONLY supports Ableton Link. I’ve now connected my Roland TR-8s via the iPhone app MIDI Link and a USB-C to MIDI adapter.
This works perfectly, although a direct MIDI connection would of course be ideal. However, only the 1850 mixer has that.
But even the competitor’s controllers/standalone units don’t have MIDI inputs/outputs.
Only Traktor Pro supports direct MIDI in/out.
This is, and unfortunately will remain, the domain of mixers.