If you are interested in getting from A to B rather directly and don't mind riding on (mainly local) roads w/o a dedicated cycle path, I'd suggest you have a look at
http://www.radweit.de/index/ybergros.html . The Murgtal-Radweg is part of the radweit route from Karlsruhe/Rastatt to Konstanz am Bodensee (or Lake Constance as you call it). I took that route as part of my tour from Kaiserslautern to Salzburg in June '15 and enjoyed it a lot. If your time allows and you prefer rides that involve some climbing (as I do) rather than following river valleys, I would recommend the Rastatt/Konstanz tour, a ferry ride on Lake Constance to Lindau (or just ride there along the north/south shore), and then follow the most spectacular (and demanding) of Germany's long distance cycling paths, the
http://www.bodensee-koenigssee-radweg.de , which you may leave at Füssen, Bad Tölz, or even Rosenheim to turn for Munich.
btw.: As for getting to Rastatt, the cable ferry between Seltz (F) and Plittersdorf is quite nice.
Oliver