Currently I am running a stock set up (6 boat speakers and roswell speaker/light bar) With a Rockford sub and amp.

What I want to do is put the kicker amp on the interior speakers and get new tower speakers and add a zld.

I was wondering which following would be better and is the hybrid system worth the extra $340?
2 pair xm9's with 1 harpoon amp or
the xm9 hybrid system with pair of xm9 and two pairs of sxt65q and two harpoon amps (is there enough room for all 6 speakers on a 21V.

We wakeboard 50% of the time and surf the other 50% of the time. only time we seam sit and change wieght set ups.

I currently run duel batterys and also looking at adding a pro-sport charger.
Will I need a third battery if i add one or two harpoon amps?