Google locates the address for the Munich drop-off location (on Robert Bosch Strasse in Garching) in the BMW factory complex. Are we really supposed to drop off our Audis at the BMW factory?

The dropoff locations are run by the shipping company E.H. Harms. The location in Garching, MADA (Munich Automobile Drop-off Agency), is a subcontractor to Harms and receives BMW, MBZ, and Porsche, and now Audi.
BTW, the location is in an industrial park area. Drive to the end of the street, and on the left you'll see a ramp and a small "Harms" sign. Drive up the ramp, turn left, and look for #13 and you will also see parking spaces labeled "Harms".

There did seem to be mostly BMWs parked there for drop-off, but as you said Harms isn't associated with any one manufacturer.