The Thing about damaging the woofer if you don't have the higher range speakers attached is pure salesman horse manure to try to sell you more. Many of us use subs with a mix down to cover the low end of all the other stops in the other channels, it is not like water into a balloon, it is just an electrical signal that will die if it doesn't go anywhere. I have used mine for almost 10 years now with nothing else attached and it hasn't exploded yet, although we've had two huge earthquakes in two weeks - maybe it was the unreleased energy from my sub. (Joking about it helps relieve some of the tension of the tragetragedies we have seen around us here).
John