Sir Al,
SPX-177R are a 2 way set I'm pretty sure.

i don't see a reason why these wouldn't handle 80hz x point with sane amount of output.

seal up the doors and make sure they are strong with not much flex. take off the plastic door panel to make sure the door itself is fine. if you get the vibrations with plastic panel on, do something with the panel, find the spot where it vibrates. some deadening may help, sometimes it is the contact point of the panel with the metal door that is making noises...
also make sure that no wire inside the door, or in between door and plastic panel is free to move, these will also make noises.