There really isnt enough depth available under the seat to do it easily plus it will be 10X louder if you give up some space in the mid cabin for the subs.
Here are 4 12's in a bandpass I did in a 28 Bullet but i recommend doing them in the mid cabin.
The Alpine amps weren't necessarily better. They were just the first ones to use the protection circuitry that continuously rolls back power output as voltage drops and temperature rises. (which was a great idea)
The Rockford amps were doing exactly what they were supposed to do to protect...
Thats not true at all. Their quality has actually gotten a lot better in the last 3 or 4 years. It might not be the equipment in your boat. Remember... system design, layout, and installation, is just as important as the equipment itself. When boat manufatcturers are assembling boats, the stereo...
Before you waste money trying to get the USB port repaired, try an iPod nano or iPod classic on it to verify its broken. The older Alpines have a problem with newer iPhones and iPod Touches.
If you do decide to get it repaired, sending it back to Alpine is your best bet.
DC is incorrect. RCA output and speaker output from both head units and amplifiers are AC voltage.
An iPhone app signal generator will work but I would trust the signal from a CD to be a lot more accurate and "clean".
Distortion usually becomes audible in the top 10% of the head units...