Now I do get an odd error message in the PD Console that suggests that it can't find darwin along with an enormous file address (can't fully fit in the console). I haven't been having too much trouble with it despite this issue. Ought I to consider doing a full re-install of the latest version of PD (as I've updated within the past year), or might I have some other sort of glitch going on?

You do need a third party app to interface that unfinished Mac midi implementation. I would recommend MidiPatchbay which I can personally vouch for as I use it all the time, or possibly MidiPipe, which I have less experience with. Like IEC, you can use those programs to create all the virtual midi ports you need as well as do much, much more such as port/channel rerouteing, translation etc.

Now that said, there's a certain trick you need to know to get it to work with Pd. You can presently only get access to the first 9 of Pd's internal midi ports with Mac OS, but they will not reliably connect to anything beyond the first nine ports on the Mac's midi port list. For this reason you must first make sure that you start out with all midi ports deactivated, then create/activate your nine virtual ports. Then (and only then) you should start Pd and connect it to the nine ports you created. You can then activate all the midi ports on your system and use the third party midi app to route to any port you like. You have to do it in exactly that order or it won't work.

I am pleased to report that there is currently some headway being made in fixing the various long standing midi problems in Pd -- Hopefully in the near future you will be able to connect Mac Pd midi directly like any other midi app without having to go through any of this redundant silliness at all.

1. Start MIDIPatchbay, create a single universal MIDI strip with both input and output - name "PD-Input"/"PD-Output" for reference. Allows all notes, allows all messages, clocks in real-time.

2. The patch itself doesn't show up in Audio/MIDI setup. That's fine, as I understand it the MIDI signal is traveling through MIDIPatchbay anyways. IAC is turned off and no software instruments are installed. I can close down Audio/MIDI setup and ignore it.

3. Start Mainstage, make sure that the volume is up, a patch is readied, and that Mainstage recognizes that there is a MIDI input available. Mainstage recognizes "1 MIDI input available"

4. Start PD-Extended and open the Sequencer patch.

5. Go through the process of making sure all components of the patch are functioning (it has a sequence tempo set, all the notes are active, volume is up, all the usual goodies).

6. Check DSP to on (I don't think it's necessary, but I tend to idiot proof my processes).

7. Set MIDI output from PD-Extended to "PD-Input" from MIDIPatchbay.

At this point I have all three pieces of software running, I believe in the correct order, and connected to one another with the only glitch being that I don't get a lick of audio. I'll dump the patch here for reference:

MIDI Sequencer Array.pd

I try to keep things fairly self-explanatory in terms of sends/receives and with comments within the object arrangement, but here's hoping it's legible. If the problem is in the coding of the patch I can take it across to that section of the forum. That said, even making a simple patch to create a note with set number, velocity, and duration on manual bang and send through the midiout doesn't seem to be arriving to Mainstage. I suppose I could use one of my other programs capable of MIDI synthesis, but that seems superfluous.

I really appreciate the help, I've worked with PD less frequently over the past five years or so than when I was first learning the ropes; it always seems like I have to re-learn a few things as well as double check on my knowledge of possible objects to use... Always something new.

1. You should probably start your Pd instance before the sound app.

2. I don't know if you are aware of this, but Pd Extended is a dead, unsupported Pd variant and has been so for a few years now. We've seen a number of posts on here from people trying to use it with more recent OS versions and reporting a number of problems -- if they can get it to work at all. I had assumed you were using Pd Vanilla. You can grab the latest version of that from here:

http://msp.ucsd.edu/software.htm

If you are using any of the external libraries included with Extended in your patch, you can search, download and install them very easily now with the included deken external wrangler assessable from the Help menu.

You can also try the new Extended monolithic replacement Purr Data:

https://forum.pdpatchrepo.info/topic/10569/purr-data-finally-released

I'll check that patch but ATM I'm on the linux box and my (ancient) Mac hardware isn't immediately available.