Mike, if you see the stainless screw heads above the sub, they are holding the amp mounted inside the helm enclosure.
Also, not sure if you can blow these up but lower right side of the last picture is a remote, so you can change stations, sources, volume etc from the aft deck.
Thanks Tom 4 the pic's.
The previous owner had 2 bazooka type enclosed speakers in enclosures mounted in the aft deck area of my '96 355. They are bolted to the 2 columns that support the hard cover over the aft deck. They sound great at the bridge and aft deck. Can be heard while swimming too. There is a 500 watt Pioneer amp below the Pioneer deck mounted in the cabin.