It's been a while since I've put together a setup (last amp I bought was probably 10 years ago. a PPI Art A600.2)

So I'm not too familiar with all the new amps out there etc...
But I'm putting a system together for my boat, and I'm looking for a good 2 channel amp to power a pair of Crystal Mobileaudio CSX 615 6.5" speakers.
The speakers will be for the tower and will only be used while wakeboarding (meant to be heard 75ft behind the boat while underway) So they will be played very loud.

The CSX 615's seem to be pretty inefficient? (the current amp in the boat that drives 4 component speakers and a 10" sub would not push these things)

Any suggestions?