Ok,
This is my theory,
Input HDV Material through firewire from JVC BR-HD50U JVC Deck, edit natively on fcp 5, output through firewire to same deck (still HDV, no downconvertion, correct?), simultaneously from component output on deck go to component input on beta sp (here is were the downconvertion would happen,) and at the same time, so I can monitor HDV material, I