Ahh I see - next time read the readme ;-)
--dev Space separated list of cuda devices
In short, not --dev=0,1,2 but --dev 0 1 2
(no "=", no comma)
Found it!
--dev 0 1 2 works in AM, but not in the cfg file
dev=0,1,2 works in the cfg file, but not in AM
Thanks for the help guys!!