Building on the good work of Patricia @Zauberelfe00 for the Elvox 8879 (also a Due Fili intercom) at Elvox 8879 as generic analogue intercom -> nuki opener, I managed to get nearly everything working.
Two points need further work from the Nuki team: (1) continuous mode keeps the lock open permanently after the first ring to open and (2) ring to open takes 30-60 seconds to unlock the door, whereas a direct open command via the app only takes a few seconds.
This is how I proceeded:
Disclaimer: I accept no liability for any errors in the content of these instructions nor for any technical problems
Solder the blue and purple wires (from the opener) to the circuit board of the 6329 as shown. If you have a 6329C with color screen, the circuit board lines are slightly different but the pins to solder the wires to are the same.
Cut one of the red wires that runs from the circuit board to the intercom speaker in half, strip both wire ends, connect the yellow wire (from the opener) to the red wire part going to the circuit board and the green wire (from the opener) to the red wire part going to the intercom speaker.
IMPORTANT: if after performing the rest of the steps, ring detection does not work when you enable ring suppression, swap the red wires that go to the circuit board by unplugging and replugging the connectors from/to the pins on the board, as shown:
Connect the red and black wires from the opener to the intercom connector print as shown:
Update the Opener firmware and app to the latest versions. Configure the opener as Generic Analogue intercom, confirm the door opening and ring to open, even though the latter will not work yet.
Contact one of the Nuki team members at developer.nuki.io and ask to activate analogue ring detection with a threshold of 9000 mV. You will be sent instructions on how to proceed.