Well in First Contact they all just fired on the same spot and that did the trick, apparently.
Of course, First Contact is retarded, like all the TNG movies.
In that case, they had Picard, who was supposed to know where the vulnerable spot was somehow, because he was once assimilated.
I know, but that's still really dumb. It still establishes that if people know where to aim (all they have to do is ask old johnny), they can all just shoot in the same place and 5 seconds later the whole cube blows up. All of a sudden the villain is reduced from nearly invulnerable force to a joke.