I would highly recommend Eurotech in New Brighton. They have been around a long time. The mechanics there have all the certifications and training of dealership mechanics, and then some. The owner, Seth Thorsen, is one of the most knowledgeable people about BMWs and other German marques. He actually travels all over the US to put on training for independent and dealership mechanics. Eurotech is also a supporter/sponsor of the MNBMW group on facebook (join if you haven't), and they host a couple meets/cookouts every year. They are the only non-dealership Dinan and BavSound dealer/installer in MN. Their prices are pretty similar to dealership prices, but they have loaner cars for customers as part of their service (F30 320i and similar quality), along with a great waiting area with free Keurig coffee, WiFi, TV/movies, and such.
They've worked on all three of my Bimmers: E46 M3, Z3M Coupe and F30 328i (Dinan package), and for non-warranty work, I won't go anywhere else.
http://www.eurotechmn.com