Also, OP, you're gonna need more than 25 feet of wire unless you're driving a motorcycle or a Smartcar. If you're driving a smartcar you should just shoot yourself and save someone else the trouble lol.
It'll probably be about 20 feet to run positive power from front to back, a foot to run the positive posts on each of the back batteries together, another foot to run the negative posts on each of the back batteries together, another foot each to run the negatives on each of the rear batteries to the chassis, about five feet to run from the alternator to the front battery, and another foot to run from the front battery to the chassis, and another two to run from the front battery to the engine block. That's 32 feet already. To power your amp you'll need about a foot from each of the batteries to a distribution block, then another foot or two for the distribution block to the amp, so like 36 feet. Then another couple feet for the amp to the chassis ground or battery negative, and it's also not a bad idea to run negative power from the rear batteries to the front battery, so another 20 feet. 60 feet might be closer to what you need, no way you'll get away with 25.