Ok got it working ...
For all who are coming next with the same problem ....
I think it will work with nearly any USB/Serial converter. At the moment I am using a Silabs CP210x Chip without any problem.
And you also don´t worry about any serial port settings in Windows. When you change the baud rate within your application, all is fine.
But it´s crucial to add a TTL to RS232 Levelshifter like the MAX232 to your connection. Otherwise it won´t work.
And keep in mind that the original serial cable is 2-2, 3-3, 5-5 regarding the wiring.
So in my case I had to cross the Tx, Rx lines in addition.
I will create a picture for that and upload it here - just for reference
But for now I´m really happy that it is working.
Oh and forgot about the original software. Since the checksum bytes are rotated that software won´t work with new KP184 devices ... Sadly ...
Dominik