Kinda depends....
How much space is above the drop ceiling? Is it close to the rafters or do you have like 2-3 feet above it?
If it's close to the rafters, you can mount the speakers to the rafters, like you would a recessed light, which doesn't really use the ceiling tile for weight, but rather "floats" above it.
Either way, you'll probably get a little rumbling going on with a drop ceiling as it settles and loosens over the years.
I know my basement ceiling rattles when we turn up the arcade or the jukebox.