It's not so much of how loud you are as much as the tunning. I'm not near as loud as Steve or Rusty but I can move a lot of air cause I'm tuned real low. Never hurts to try it out.
It's a factory 90amp charges to 13.6 all day.
2 batteries won't kill your charging system. Maybe in the long run but not if your smart with it.
Alts tend to go you when the battery has let go and now the alt is tring to make up for the loss of battery charge. I tend to see this with the cheaper batteries.
I use an external bass knob on mine not those cheapo' that come with some amps. Those seem to just work on the bass boost on the amp but don't really have any control. i've also noticed that it will boost the noise with the bass. What I have will take the amp signal from 0 to 100%
http://www.autosound2000.com/linedrivers.htm N-22
I have done that in the past. I use 60 hz to set or gain match my amps. I do like to keep from giving my customers full tilt on there stuff. That way it will last longer. Some people do not have self control so I use good judgement for them.
You'll want to run both a postive and negitive to your rear battery. Fuse that run close to the rear battery and fuse it at the front battery. Then run your power and groung from the back battery to the amp. make sure you use the proper size wire. You should be fine with the factory alt as long as it is working well now. I run 13 batteries of a factory alt with no issues.
Box is all me, I did have it sprayed by someone else. I can spray but I'm not setup to do it yet. New shop is on the way! The amps are mounted down both sides of the box so they can't be seen.