FWIW, I have some of the same thoughts/objectives about using Digitakt live (with guitar and voice) as OP. With firmware 1.06 I was able to connect a MIDI cable from out to in of the Digitakt and change patterns using MIDI triggers in the penultimate pattern step to queue up the next Digitakt pattern. So this will work if your song has 16 or fewer patterns. I also thought of the KMI SoftStep as a way to trigger live. Hadn’t thought of using the TC Helicon to control the Digitakt but I can see how this could work. My interest of the Digitakt over OT mk II was cost, ease of use, waveform view when editing trigs, size, (future) software support, and some comments I’ve read regarding superior sound quality–though I haven’t A/B’d them.