I have quite a bit of information on the Boonville Missouri Gantners, including some information on Diringer, Stretz, and Garthoffner. Andrew was my great-great-grandfather as well.
I would particularly be interested in any information on Margaret Gantner, Andrew's sister, who married George Stretz. Or on their father, supposedly named Ignaz Gantner, who I believe stayed in Baden.
Link to my tree:http://www.genealogy.com/users/g/a/n/George-Gantner/
I also recommend Jim Thoma's excellent website, with amazing numbers of Boonville residents:http://www.thomafamily.org/