All,
Please refer to this article on Ableton website with regard to setting up a “Virtual MIDI Port”:
Once this is set-up, in AudioModern devices a new port is displayed inside the plug-ins. Assign your Riffs/Tracks/etc. to individual MIDI channels and then put your soft-synths, etc. on MIDI tracks as normal but use the input from IAC (on Mac) and select corresponding port.