I still haven't had any success figuring this out. Any more ideas?
Sure… anybody around here can tell you I'm just chock full of
shit ideas.
When last heard from, you were going to check cable(s). Assuming you did that…
I suspect at this point, having spanked all of the software without success, that it is indeed time to start poking at your hardware.
The cable(s) were a natural place to start/check, although unless they get tugged on regularly they're not normally very likely to cause issues.
It
seems from here that you have an issue with MIDI in
one direction between the MTP and the G4. That was confirmed by Clockworks not seeing the interfaces when you ran setup again.
I say one direction because that was the original symptom: you could broadcast MIDI
to devices but couldn't receive any
back. Also, identifying interfaces with either Clockworks or OMS requires bidirectional communication - a failure to receive an response from a connected interface will be interpreted as nothing being there.
It seems clear (of course, it's easy to be certain about stuff from here…) that you have a hardware device issue. Either the Timepieces, the Griffin modem port doohickey or…oh wait, that's pretty much it.
You were able to briefly get MIDI from a directly plugged DX7 but that later failed. THAT is telling you something is sick along that road.
The very first step is open the G4 and poke and prod the Griffin. Clean the contacts on the connector. Liberally clean the plugs and connectors on the MTPs also. Say a prayer and see what happens.
If no joy, you have a problem. Without
serious service equipment and documentation you can only test by substitution. I suspect you do NOT have known-to-be-good spares of these components on the shelf… or do you? If you
do, you're both smarter and wealthier than I am.
So, what to do? Pull the stuff apart; Try to set of the very simplest path from the G4 to a test instrument (like the DX) you can. If you have another old known-good interface of any kind, try it. If you can reliably get MIDI to and from the G4, you'll have eliminated the Griffin as the culprit. Then try the MTPs one-at-a-time - maybe one will work and the other not. OR… maybe they'll both work individually but not when connected together.
If you're living right, you'll be able to narrow all of this down to one device and you'll then know what to do.
Be meticulous and thorough; suspect everything; trust nothing, and most of all…
Good luck.