Tower speaker amp suggestions?

Have 4x skylon vector8 tower speakers on our mb tomcat running into a kicker 4 channel 400 watt amp. Pretty much when anyone is surfing or wakeboarding no one can hear the music coming out of the speakers. Don’t get me wrong they are loud, but not when your 40+ feet behind a running boat. I originally installed a wet sounds ws-420 which helped in preventing the in boat speakers from crackling and what not, still though just seems like Im not getting enough sound of of these tower speakers. Would really like to hear them better for the towed rider.

Boat also has the factory wetsounds 6 channel amp that powers in boat speakers and baby sub. Also have a JL-1000 powering a 13.5 w7 sub.

Bought the boat from dealer with the crappy kicker amp, really want to know if adding a larger amp would improve volume dramatically. Also any amp suggestions as there are a sea of them out there would be very much appreciated.