Well you did'nt tell which DAW you had before, so i don't get you write "still hoping".
I don't use Live, so i can't give you a step by step guide. Basicly the procedure is the same as for routing audio into any other instrument, so it's mostly a DAW question.
I know Live's channels have "Audio From" and "Audio To" selectors, and they are probably in use. Perhaps involving Sidechain feature.
If you wan't reply from an exsperienced Live user, then i suggest you ask in Ableton forum. But i i actually don't think it's that difficult, if you just load Arturia MS.20 in Live - perhaps in VST3 format. I can not use VST2 in my DAW Studio One, if i wan't to use the external audio in feature. But then it's just to use the Sidechain feature Studio One have now to get things like this to work. Quite simple really.