Thanks for the supportive post. 
Actually I am runnig a dual stack 7.4 PO here ,so the B2B addon is not part of the solution.
The IT managment was in favor of my solution (regarding SNDPRN,SNDPRT) and so forced it.
We are now also benefit from common X12 message mapping with maximum reusability and so our EDI implementations are super - fast.everyone is happy.
For this kind of implementations I have been practicing my whole proffetional life as a SAP PI architect...everything is falling into place. 