Which processes can SAP PO 7.5 be used in new implementation of SRM Extended classic scenario

Hello,

We are in process of doing a new implementation of SRM public sector extended classic sceanrio. I would like to understand the use of SAP PI in different processes of SRM when integrating with ECC and with SUS. The debate is in between use of RFC or use of SAP PI as mode of connection. Please help me with some specific and clear details that relate to Public sector/ ECC-SRM-SUS/ Extended Classic Implementation.

My question is in terms of the below screenshot where I see different SRM processes such as contracts, PO, etc.