So what Ed did for me was have me record my stock ROM and send it over to him, I of course kept a copy for myself in case I ever needed it / wanted to compare. Additionally, the XML file he provides, he told me exactly where to place it. Per the E-mail he sent me:
"Please put the .xml in the following location:-
C:\Program Files (x86)\OpenECU\EcuFlash\rommetadata\subaru\Legacy 3.6L\"
Obviously your path may be different towards the end, but in general, this should give you an idea.