Since the 6.0 release, I see the rapid board is the preferred board yet I see no way to really work with epics.
If an epic is in the backlog, I can't see what stories are associated with it.
If an epic is on the task board, same. It just shows the epic as any other issue sitting by itself.
I don't see any way to edit the epic to add stories to it from the rapid board either.
So all I can determine is epics are only manageable via the old (classic) boards though those are on their way to being deprecated from what I can tell.