I found those websites myself and I’m under this impression too, that the programming key was a hardware device at the beginning. This is why I asked in my first post if it was some kind of an EEPROM. The remote control itself acts as a programmer, with this programming key connected to it. For those who remember the PMC programmer, it had indeed EEPROM modules for Siemens, Phonak and Hansaton, and for the operating system as well.
But, according to the instructions available in Widex Compass 4.6, a cable is needed to connect the right port of the Hi-Pro to the programming key port of the remote control. With the remote control acting as a programmer, I suppose the situation is somehow similar to programming a Siemens Swing HA with the PMC, using the EEPROM module. Nowadays, nobody does that, since the Hi-Pro can be used to fit Siemens Swing HA’s and I suppose this is also the situation with the Widex Quattro.