wait, so you have 10 6.5 speakers total? 4 on the tower and 6 in the cabin?
my boat has 4 6.5's and a 10w3 sub that is all powered by one 6 channel jl audio amp. that does a fine job but you will need at least 2 amps, probably a 6 channel to run the sub and tower speakers, then a another 6 channel to run your cabin speakers. the 6 channel jl audio marine series amp puts out 70 watts RMS to 6 channels at 14.5v.
you may want to run 3 amps though so your sub gets enough power. so in that case you should get a 6 channel for the cabin, 4 channel for the tower, and a mono amp for the sub.
thats just my opinion, theres some people on this board that know a hell of a lot more than me about audio.