Ok. Cheers for the detailed reply. 
I haven’t checked yet, but, if feedback’s an issue, that could be causing it. I will look into it and get back.
What do you mean by ‘ports rather than channels’?
To clarify, so, when you open an external midi track in logic, you have the library open on the right. I have IAC Driver From Logic, From Renoise (I named them the same as you before you posted this ), and Renoise Midi-In (among GM device and my audio interface, etc). In each one there are 16 channels. What I want to know, is, is channel 1 in IAC from renoise, the same channel as channel 1 in IAC from logic, or renoise midi-in?
And, what’s the advantage of setting up an IAC from logic (to renoise) rather than using the standard Renoise Midi-In, that comes up? Renoise Midi-In seems to work fine.
Also, as a fellow mac user, you might be able to help with the following (or at least benefit if I find a workaround):