Thanks a lot for your prompt replies!
As for now, without the OT, I’m launching the voice clips from Ableton Live with a midi keyboard (Arturia Keystep, very versatile piece of gear!). With the OT, the goal of playing computer/dawless will be acheived 
The Keystep will definitly be plugged to the OT and I will take the midi processing route.
I don’t think I’ll have slot emplacement issues so, if I get it right, the main reason for using slices vs slots would be “use lfo / crossfader to change them in realtime” ? I don’t really understand what you mean so I started reading this : LFO´s... what are in them?, quite dense, I’ll get back to it when I’m more familiar with the OT …
The plan will probably be for each bank/song to have a track, disconnected from the sequencer, with sample locks containing the different voice clips and figure out the midi way to freely launch them from the Keystep.