The Munchener Marriott in the Berliner Strasse 93 has a parkway on the backside, to the left and right are business buildings. Accross the street there is a larger residential area with mostly larger apartment buildings.
We are there quite often and also do not want to have to pay the steep parking prices. We usually unload/load in front of the hotel in the circular drive but then parallel park either across the street or in one of the side streets across from the hotel. You might have to drive around for a couple of minutes, but it is worth it.
We spent a week there last X-Mas and were always able to find a parking spot. We have never had any problems with security or damages to the car in this area.
Hope this help! Have a great trip.
BTW - The sports bar "Champions" located in the hotel is GREAT !!!
BTW - The next underground railway station is about 200 yards from the hotel. You can purchase a family ticket for around 8-9 € which is valid until 6a.m. the following day. This saves quite a bit of money and stress when traveling within the downtown area.