I still suggest a through-bolt with a large washer and double (locked) nuts above.

Even with your sub on his or her feet, they can wilt or collapse, both out of desire or out of need, and the last thing you want is something to pull out of the ceiling... perhaps even bringing down debris with it.

And once you have any sort of suspension point, you will use it more and more often. Guaranteed.

Might as well do it right the first time.