mettelus
I have only been able to use hardware assignments in MV. Some soft synths pass their own MIDI, but could not get "MIDI learn" to accept these.
I had to be more precise, and EXTERNAL MIDI Loop software is required to "MIDI Learn" Matrix. For Software synth MIDI output to be used, it should be routed to some dedicated MIDI track (as the only input), with "ECHO always on" and the output set to external "MIDI Loop". Than this "MIDI Loop" as input can be used for Matrix.
To avoid "MIDI leaks", install my AZ Controller as a Control Surface, with the input set to "MIDI Loop" (the output to "Note"). In the Options tab change "Block assigned MIDI messages" to "Block all channel messages" (that is the only setting required for this use case). After that, you still can use "MIDI Loop" for Matrix or other "Remote control" in Sonar, but nothing from it will "leak" into normal MIDI tracks. But watch out if you start Sonar without first starting external MIDI Loop! Sonar likes to "forget" the input assignments for Control Surfaces, AZ Controller will no longer "block" "MIDI Loop" when it is available again.