I am comfortable with the SRT 6's being an AMG just as much as the AMG32 is.

In years gone by it was common to see coach built automobiles. Rolls Royce, Dusenberg, Packard, Mercedes, etc would sell their cars sans body and interior to coach builders. Those cars were still called by the chassis maufacturers' name with a "by Fisher" or "by (insert the builders name). Karmann is a coach builder. By the way, those special coach built cars are generally held in higher regard than the manufacturers' own bodied cars.