@vidasonik

Could it be a case of Ableton not sharing the device? (I know this can occur with Asio in PCs).
It can get a little complex once you have a number of Multi-output and/or aggregate devices. 
A screenshot of your Audio MIDI setup would be helpful since I need to walk through the signal flow.

@dusx yes, thanks! I've done that and seems to work also with the 'Multi-output device' which is another option (along with aggregate device) in the Audio MIDI setup. I guess I'll have to use one of these!

Cheers, Dave