Just to note that this is proving essential as an approach to get MIDI data routed from an Audio Unit implementation.
First-off, the user must enable their Mac’s IAC driver using the built-in “Audio MIDI Setup” application (normally this driver is disabled by default for some unknown reason!)
The Filter’s UI component needs to present the user with a list of available MIDI output devices (given the changes I outlined earlier in this thread, the IAC driver is listed automatically by Juce!). The MIDI effect AU needs to send its data via this output device/port. From an audio perspective, the AU “that is really a MIDI Effect” would otherwise simply pass-on silence, or passes-through the input audio data.
The MIDI data can then be rendered on another MIDI track in Logic by taking data from the MIDI input device presented as an IAC port. NB this approach would also allow a MIDI effect to be deployed as a VST on a Mac, even where the platform doesn’t support MIDI routing through VSTs (e.g. Cubase).
As an alternative rendering strategy, or if punters simply must play through Quick Time Musical Instruments :), punters don’t need to use the second MIDI track, but could instead use the free MidiPipe application by SubtleSoft, to route data from Midi In (presented as IAC Driver - Bus 1) and output through e.g. the DLS Synth.
Anyways, hoping this helps!