If I'm using export buses, than should I use bi-directional, insert or extract?No... You need to use and export bus on the DSU first. Then once the export is complete then remove it and attached the storage bus. I also recommend you configure the storage bus for a higher priority and the item stored.
You need to look up some guides on how ME storage works. The ME system will NOT under any circumstance move items around inside its own storages once it is already inthere. ME storage bus' allows you to make inventories like barrels and chests be counted like they were part of the ME storage. All the settings of a ME storage bus(priority, directions etc.) deal solely with items entering and exiting the ME network. Upon this threshold is when the location of storage is decided, based on a large variety of factors like Priority, already present items etc.How ever hard I try, I can't seem to get the storage buses to extract out of the ME system into a DSU...
I've tried all the different modes and none seem to work?
Do I need to give the buses different prioties?
No sadly that is incorrect. As long as there are items already in a storage device, that will be where the items will go (back to). Doesn't matter what priority is of other empty storages.configure the storage bus and priority and use an export bus to a interface to export the items
AE will take out from the lowset priority and push into the highest priority it will fit in,