Dear Marcel,
I believe you are indicating at PO Automation feature of Ariba. We are planning to implement that. It is a standard solution of Ariba. There is a configuration you need to do to create end points in Ariba Network Buyer Side and set up the document routing configuration also.
Apart from the above, at the SAP ECC or the ERP side also, you need to import certain transports and hence do certain configurations.
I think I have some integration documents about this. Let me know if you would like to have those documents. Or else you can download from Ariba Connect.
Regards
Sangram