Wow, great topic. I have been having a hard time finding much information about boat stereo. I went to a couple of shops in my area (Santa Rosa) to get an estimate, and they wanted soooo much money to add some tower speakers and a sub to my 6 speaker (6 1/2 Sony Xplod speakers with a 4/3 channel Sony Xplod amp) factory setup that I just couldn't believe it. They also said I wouldn't be able to use the current alternator in the boat and would need a $650 upgrade there just to get started. By the time they were done I needed the entire boat rewired, all new speakers, 2 tower enclosures and a 12" sub with a new 5 channel amp, new head unit, extra battery and $7,000. I wouldn't even spend that much on my home stereo AND I LIVE THERE.
So I bought four kicker KS65s in AudioFormz Illusion X compatible enclosures, connected them in series to two channels of my current amp (and disconnected two of the six factory speakers) I have the tower speakers on the rear fade and the boat speakers (dash and front) on the front. I used the amp's high pass, gain and low pass filters to balance it all out and it sounds decent. However, I need mo bass. I checked with Malibu directly and they say I have a 90 amp alternator already. I've got two deep cycle batteries and a selector switch. I could try a sub with an enclosure box under the passenger side of the cockpit (where the batteries reside) and cut out a port in the passthru between the back and front of the boat to let the bass out, and could get another amp to power it, but how do I control the volume and balance for the bass and how do I hook both amps up to the head unit. I've looked at lots of web sites and they are either all fluff or too technical for doing it yourself. Any suggestions appreciated.