[Kraftwerk] Sennheiser, Vocoders, Kraftwerk, and Privileges

Greetings Everyone... I am an electronic musician and I am deeply influenced by Kraftwerk. I am most infatuated by their use of vocoders. Apparently, they used the Sennheiser- Does anyone know in detail the story about why and how they came into adopting this specific one? It seems that this particular unit was rather expensive at the time- how did kraftwerk manage to obtain all of their equipments? Were their parents rich? [w]