I have had this knowledge in my head for a long time now and thought it would be better to write a diagram to explain the current setup for my MIDI routing.
I use MIDI routing one way – MIDI OUT – from my UMC1820 sound interface.
I have two keyboard controllers, one next to my computer, and one next to my Eurorack, that are attached via USB to my computer which I route the notes via Ableton to the MIDI out of the UMC1820 interface.
I then selectively record the synths that I want to record. I don’t use MIDI channels, everything is making a sound at once when I press a key on the keyboard controller. I just record the hardware synths that I want to use in the track.
If I want to use multiple hardware synths in a track then I do multiple MIDI tracks and multiple records.