Pretty stoked that I finally got this working. I ordered a RetroKits RK-002 MIDI cable ($65 shipped from EU, btw) which allows you to distribute polyphonic MIDI data across multiple channels with one of its firmware modes. This effectively means that the Digitakt can now become an 8-voice polyphonic sampler/synthesizer! And I have to say, it works pretty fantastically.
For testing I have been using some SCWs from the Prophet VS (easily found on Google for those that will ask) and creating my own voices by layering 2 or 3 waves and resampling them back to one track. The result is simply amazing and sounds fantastic. You can see a quick demo on my Instagram: