I just got os9 Loaded on My mini and load in OMS and the driver to My Tascam US 224. But it is showing 3 US 224? When I do a midi test for the set up I get no responce. I don't want to do a reinstall of everything. My Ste up goes from a Mini to the US-224 Then to a Studio 64X And Splits to 2 Rack Syths and a Kurzweil and in a USB midi interface and to My Macbook Air. it was tricky to set up using Tiger midi/Audio. and High Sierra midi/audio is a breeze to set up. But I want to use Studio Vision and Garage Band for Kontak... and still have 64 midi channels to work with.
The "three" 224s you see are probably as described below from the Tascam manual:
"When the setup is complete you should see a list of all your connected MIDI ports.
At the least you should see three icons pertaining to the US-224 specifically: the US-224 icon, US-224 MIDI port and US-224 Control port."This is page 14:
https://www.manualslib.com/manual/326917/Tascam-Us-224.html?page=14#manualI
think I followed your setup at least until you got to: "and in a USB midi interface and to My Macbook Air"
AND "But I want to use Studio Vision and Garage Band for Kontak"
It seems (hard to tell) you want to run your Air AND the Mini
at the same time. ( ?? )
If you haven't yet, I suggest you strip everything back and start verifying one at a time. Say, use OMS manual setup to hook ONE US-224 you see (the MIDI port one) to the Tascam to a synth and see if you can get MIDI through that. If you can, add the 64x and try again and so forth reassembling stuff piece by piece and see where it gets stuck.
You're trying to marry OMS with Core Audio / MIDI, OS9 with OSX and ??
Or do you just want different setups to use separately? It will require a much better description of your setup and objective - for me at least - to offer any really good advice.