Hello there guys. I am a total newb when it comes to building a system. But I'm giving it a shot. I have a 2006 Chevy Silverado extended cab. So far I have installed a Kenwood KDC X997 head unit, Focal integration 6.5" components in front doors, Polk 4x6's in rear doors, and two Polk 8" subs in a prefab box under rear seat. The Focals are powered by an Arc Audio KS300.4 amp. The Polks in the rear door are powered by the head unit. The (outdated) subs are powered by a (outdated) Phoenix Gold Octane R-4.0.2. I want to replace the subs and box. I was considering going with either 2 or 4 of the DD shallow 8" subs in a ported box that i can have made in a local shop. I haven't decided on an amp to power them yet. Any input on a compatible amp? And is 4 subs overkill or will two 8's be enough? I'm looking for SQ over SL. I listen to everything across the board but mostly hard rock. Any help would be greatly appreciated. Thanks in advance.