How Do I Adjust A Subwoofer For Best Sound?

The more I drive the truck and listen to it....although it sounds a LOT better than those two 6 x 9s in the those tiny boxes, I'm thinking the front speakers are over powered by the subwoofer.
A separate amp is almost alway gonna be better and louder than the head unit built in amp,

It’s relatively way easier to get volume out of subs than the front end, especially if powering the front from the deck.