So i used AUM on ipad(a mixer/daw like app with as many channels as your dsp/cpu supports).
Then all midi where sent from few Digitakt tracks to synths on ipad, and since ipad can send midi/audio over usb, those synth sounds were routed back into Digitakt Main output/Headphone Output(i had few synths, bass, lead, pad, some Foley, plus send/return effects)
I mean now that i think about it, i think you can use Digitone as a audio interface and do the same like i did with ipad, but with your computer.
Saying this, since you are using Live, and will record all tracks in Live, why do you even want audio from vsts back in Digitone?