The SYN-6 is going to be the only 6 ch amp that is going to be enough power on the in boats and towers in a single amp solution. Since it is a hybrid and has two different power sections with 60x4 and 155x2. With chs 5-6 being high pass or low pass capable. What is also really cool is the flexibility of this amp. You can add a 2 ch later for the towers and bridge chs 5-6 in low pass on a sub for 600x1. Or you can add a 485 and create a 3-Some on the tower and turn the SYN-6 into a 3 ch amp for 200x2 and 600x1. So it gives you a lot of flexibility to expand
Most other 6 ch amps are going to be even power across the board like 60x6 or 75x6 etc....So you would be good on the in boat side but not enough on the tower. And other 5 ch amps are designed for coax and sub duty with the 5th ch being low pass only.
So you can compare cost of the single amp solution to other multi amp solutions and it might be a good value for you. The most power Wet Sounds option would be the SYN-4 and SYN-2 combo
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and I can see if there is a dealer near you so maybe you can go look and listen to some options and see what works best for you.