+1 to the Alsace route. Munich to Alsace was an easy 4hr drive (this was on a Saturday, so not much traffic around Stuttgart). Alsace itself was stunning. If you like wine I highly recommend visiting Marcel Deiss, near Bergheim if I recall - he's making some of the most interesting Alsatian wines out there.
From Alsace you can easily make Burgundy in 4-5hrs, then south from there through Lyon as others have said. IMO French toll motorways are the best in the world. They're in great shape, the speed limit is a quick 130km/h, traffic isn't bad, and the rest stops are clean and offer decent food.