Hello @M-Musel, I think this is not possible. Digital inputs are connected directly to the GPIOs of RPi's processor. You might be able to control only Relays/Ai and 1Wire but the rest will not work - I am also not sure if there are any I2C devices in the Pi-Top so you would have to make sure the addresses would not colide with I2C devices on UniPi.

You also cannot connect two UniPis together via the I2C