Whether your pods have single or independent connectors, you’ll have four total conductors run up the tower and two channels of amplification running the four tower speakers.
We use a ton of Polk DB651s. They’re brighter and more efficient than the Polk MM series (used frequently also) which are a little smoother, warmer, handle more power but take more power to run. This makes the DB series a better fit for tower speakers while the MM series are really an upgrade ‘in’ the boat. The Polk DBs are great used in multiples if you want quality sound when you’re at rest or beached and without the competing engine noise and wind. And, they’re decent for the rider. But, one pair of proaxial-type tower speakers (WetSounds PRO 80s or Bullet 770 HollowPoints for example) will clearly project better at 80 feet when competing against exhaust and wind. The only qualification would be that proaxials are properly powered. So you will invest a little more in both the speakers and amplification.
Your amplifier choices should be dictated by your final choice of tower speakers and subwoofer. A JL Audio G4500 would be a good place to start to drive two pair of Polk DBs on the tower and a single 4-ohm and relatively efficient sub. There are bigger and better amplifiers but this gives you balance and value. And, if you opted for proaxial tower speakers you would select a more powerful amplifier.
Hope this helps.