Argentina by dual citizen

We are beginning the adoption process in Argentina. I am blessed with dual citizenship. Though I have a great contact in Buenos Aires who will guide me, I'm not sure how to proceed w/ the U.S. end of things. I know that I need the home study and the 600-A but what else? I'd hate to get down there and be told at the U.S. consulate that they need something else from me. And if I get an attorney here to help me, will he have the specifics of what the requirements will be for the 'foster' visa for a child from Argentina (there's a 6 month guardianship period).