traveling from Stuttgart to Aix-en-Provence

I used the train recently to travel to Aix (although within France itself)- as with Avignon, there are two different stations depending on whether you use the TGV or not, so if you use the TGV (it's located further out) you need to also factor in time for the bus (or taxi) to your destination, if it is in the city. For example, In Avignon, I was lucky and just caught that "shuttle" bus with seconds to spare- otherwise I would've had to wait another hour...also, Marseilles as a tranfer point was almost always paired with Aix. My other suggestion is to see if you can get another option(s) trying Marseilles...then check Marseilles to Aix separately. (It was usually a bus, but it went back and forth quite often.) I hope that helps, a little, until you hear from someone whose done just what you want to do!