My 2nd printer is an A8 and runs very well with S3D. Absolutly no problems with it.
What the difference to A 8 - M is, I don't know, but all dimensions are identicaly to the A 8, only it has added a 2nd extruder.
If there is no own profil at the moment ( perhaps to new) , it is sufficient to add an 2nd extruder (T1 named) and its offsets (i.e. X = 20)
I'm really not an expert for such problems, but the issue may be cause by a lot of factors, i.e. the usb-cable is to long, problems with the com-ports, defect printers mainboard a.s.o.
For the experts it is very helpful to know more informations, such as the printer has worked before and the issue is new, what new components are mounted or other things have changed ...
I recomment to test it with a android tablet / smartfone and a software like this: GCodePrintr lite to be downloaded from the Google play store. On this way the issue can be isolated.
I'm using exclusively cards for both printers. Problems are unknown.