Not an answer to your question, but and alternative option to have a GUI without the screen, as long as you connect the Pi to a local network (e.g. from your router) where you can connect your phone/tablet/computer, even from another room.

https://github.com/robert-rc2i/ptq-client-webapp

https://github.com/shuhaowu/remote-for-pianoteq

Obviously this might or might not work for you, but worth mentioning in case you were not aware of this possibility.

Thank you! I was not aware of this. It's good to know but it doesn't seem to help me with this. I want the setup to be free of displays in general (and only use a pad controller as a kind of 'quasi screen').

https://github.com/robert-rc2i/ptq-client-webapp

https://github.com/shuhaowu/remote-for-pianoteq

Obviously this might or might not work for you, but worth mentioning in case you were not aware of this possibility.

Problem: I'm running Pianoteq 8 STAGE on a Raspberry Pi without a screen. Furthermore, I'm using control changes (cc-s) to control a master for Midi Tuning Standard–Extrasensory Perception (MTS-ESP). However, I end up having a very small range of notes (i.e. difference between the note with the highest pitch and the lowest) above, say, 24 notes per octave.

Questions: I could upgrade to Pianoteq 8 Standard to make use of the full rebuild option. However,
- Full rebuild does not seem possible in the 'MTS-ESP mode'?
- It only seems possible if I first import the MTS-ESP tuning?
- Is there a way to use cc-s to control the options 'import tuning from MTS-ESP' and 'full rebuild'? (I could potentially write a wrapper script.)
- Or could they be run automatically upon reception of a new MTS-ESP tuning?

What I've tried: I've tested Pianoteq 8 Standard demo and a purchased Pianoteq 8 STAGE.
- Full rebuild and import tuning from MTS-ESP doesn't seem to have any midi assign or midi learn functionality
- According to --help, they don't seem to be available in the commandline tool
- There doesn't seem to be a keyboard shortcut to access these options?

What I might try next: I could make a wrapper script that acts as an MTS-ESP client that converts the frequencies and notes to pre-note pitchbends in a midi polyphonic expression (MPE) way. Using MTS-ESP to MPE conversion does seem like a kind of roundabout solution when Pianoteq already supports MTS-ESP though ... (Potentially I could try using several midi channels in MTS-ESP, but that sounds even more complicated.)