Calling a Store Procedure in AS400 from PI/PO

We have following need:

1. We want to get some data from AS400 in to PI.

2. Transform the data

3. Send it back to AS400.

I have following questions:

1. Is PI the right tool to accomplish this?

2. Why we are not able to run Store Procedures in AS400 from PI ?

3. Should we continue trying in PI (Store Procedures) or use ABAP in stead to accomplish this?

Any help would be highly appreciable.