Thanks for that info!
What I'm trying to do is use a third party midi fx plugin called Thesys, a step sequencer, to send midi data to an external hardware instrument.
In Logic, I can get this to work using the external instrument plugin.
I just tried using an External Instrument Channel Strip in Mainstage and I can't seem to get it to work. I have my audio unit set in the midi out, using the correct midi out channel (same as I had it configured in Logic)