Here I found the decisive answer:
Originally Posted by Harakhti
[...] Microsoft added a driver enumeration for USB 2.0 in Windows 8.1 which makes it impossible to use the Samsung Odin protocol as it's called invalid and technically impossible to bypass. Sony changed its own drivers to fix the issue.
That's why I don't like this Win8 crap ...
So you can try it with a installed WinXP in a VM
and you will most likely have success (if you can not borrow an old machine with WinXP)!