Here's my setup. Sony CDX-F5700 in-dash CD which has 52Wx4 pushing 3-1/2" in dash and 4" seperates in the door (I've had the car 23 years and cut the door panels back-in the day, so no hate mail please). In the trunk I have an MTX 50Wx2 on 6x9's and 80Wx2 on Punch 10" subs in a small box facing the rear seat. There is also a 10-disc CD changer that no longer gets used thanks to the I-Pod that I've hooked directly to the aux inputs, which sounds much better than through the radio.
I've always had subs in her and can't imagine playing AC/DC's "For Those About to Rock" without 'em! Just wouldn't do it justice! All speakers except for the subs are JBL. You won't hear me from blocks away, but it crank's quite nicely with the relatively small amount of power that I'm using.
I have found that unless I have it cranked the 70 amp alternator handles the load. If you overdo it, a capacitor can be added to handle the hits that the amp makes on the system with the bass notes. The most critical thing IMO is using good wires for the connections and proper routing to eliminate noise. Get power from the battery to the amps using proper ga wires, never through the fusebox. Route power wires on one side of the car, inputs on the other. Oversize speaker wires with the finest /highest count threads and soldered connections.
Hope that helps.
