I am struggling with it as well, so far I only managed to map Spectrasonic Omnisphere manually, i.e., with the VSTi open in Ableton, right-click on the control to select learn CC/note and manually wiggle the knob or press the button you want - but it is a tedious process - and if you forget to save the settings like I did, then you need to start all over again ;-( There's got to be a better way - still looking...
