Hello Hubery,
While using PI 7.1 you would have used communication between Integration Engine of Backend to Integration Engine of PI.
But now since we have a Java only Single Stack , we have to communicate between Integration Engine of Backend to Adapter Engine of PO.
For that you have to make the changes in Backend in SXMB_ADM -> Integration Engine Configuration -> Provide AAE Destination.
In PO, You can use sender SOAP Channel with XI3.0 Protocol.
Regards,
Ruban.S