Driven has what is commonly called "lath" screws, used for stucco work.
(memory) #4 pan X 1/2 would be what I'd recommend for speaker to backbox. #6 X 1 1/4 for anything that needs to go into an anchor. Don't use the "split" anchors/rawls that everyone seems to use, they pull straight out of the wall. Use Zipits or other similar anchors. Rawls or hollow wall plugs are really for a masonary application.