MIDI Monitoring CAN be turned on and off like Audio Tracks. If a track is disarmed (Record or Monitoring) you cannot record on it, or hear live playing through it (unless the keyboard also has local sounds and is in local mode). The catch is, if you have an outboard synth in local mode, and it’s also being triggered to make sounds via MIDI events on whatever channel it also sends MIDI events, and if CuBase happens to be routing the thru back to the same ‘listening channel’ of your synth, you get ‘double triggering’ of every event.
You said your outboard gear cannot be changed between local and remote controller mode…and global MIDI thru is something different. There are options to configure the global MIDI Thru behavior (such as filtering certain types of events for recording, playing, etc.).
If you could put your board in the controller only mode (so it makes no sounds at all unless MIDI events come into a MIDI port) it should work fine with default CuBase MIDI thru settings.
In local mode it’s always going to make its onboard sounds and/or react to controls locally, with our without MIDI thru enabled.
The MIDI Thru toggle I told you about seems to be at a global level in CuBase. It’s a quick way to block all MIDI thru. When ‘deactivated’ you’ll see the MIDI input meters bouncing in CuBase when tapping keys/moving pots/sliders, and it’s even possible to ‘record’ all those events, but they never pass on through the pipe line (only playing/recording tracks, with the transport going, make it out in this case).
You might try ‘filtering’ CC messages in CuBase Preference for MIDI thru. That might be enough to resolve your continuous controller issue while keeping the record/monitor track icons working in a more user friendly manner.
Off the top of my head, it seems like toggling the global MIDI Thru as needed is likely simplest option. I.E. Turn the volume down (or mute its inputs in CuBase) on your board and enable MIDI Thru when working with VST/i or other outboard gear tracks. The Record/Monitor buttons to arm/disarm tracks must still be toggled as needed. Turn the volume up (or unmute it’s inputs in CuBase) and disable MIDI thru when working with onboard sounds in your synth.
It’s difficult for me to predict the best settings for your setup since I’m not trying to use it, but it seems to me that through some trial and error, you should be able to eventually find the magic combination of settings to sort it out for a more user-friendly experience.
If there is no way to put the board into ‘controller only’ mode, then there might still be a workaround. I.E. If it is a multi-timberal synth, you could have an empty or muted preset in one of the channels, and swap to that channel on the board itself to ‘play/record’, while CuBase reroutes it and sends it back to channels with active/unmuted presets. CuBase has options to block MIDI thru for only a specific channel, and I could go in and use that at the point I want to enable that ‘last channel’ in my synth with a working sound.
I’ve been here before, as I once had a big workstation synth that did not have a controller only mode, but it did have 16 channel ‘performance’ patches, and I could control what, if any sounds were on each channel, and what channel the keys and such would SEND events over. It was kind of a strange setup, as that particular board sent MIDI out through the internal sequencing engine first (each individual channel had to be either local, or MIDI).
Some boards that are not multi-timberal with some form of 16 channel performance mode, still have a way to change the MIDI out channel of the keys/pedals/continuous controls so it’s different from what the synth is listening for to trigger sounds via MIDI. In that case, it’s a round about way of putting the board in ‘controller mode’. Just make sure the keys/sliders/wheels/pedeals/pots/etc. send on a different channel than the board listens for triggering sounds via MIDI.
If the synth is monophonic, is ‘always local’ and ‘always in OMNI mode’ (active patch receives MIDI on all channels), I’m afraid you might always need to fiddle with some things manually on the CuBase side (key combos and macros take some of the pain out of it) as you work with different tracks/instruments. In this case, if you have a different keyboard to use as your main DAW controller, it’s probably better to do so, and move the ‘monophonic, always local, always OMNI’ synth to a ‘slave device’ position in your setup.