The ideal recommendation for path to a better sound setup would be following the steps below.

1. Decent HU capable of at least 2 pairs of RCA outputs and crossover control(optional as most amps have it as well)
2. Component set
3. Sound deadening on front doors or at the least minimum, speaker mounting locations, at least double layer(1 square feet on the inner metal behind the speaker, and 1 square feet on the panel where the speakers are mounted）
4a. 2-channel amplifier to power the component set
4b. Add on an amplifier and subwoofer complete with enclosure(box)
4c. 4-channel amplifier, front channels to power the component set, rear channels bridged to power a subwoofer.

Note that I didn't specify any rear speaker upgrades as they are not needed in a regular sedan/hatchback setup. Adding on rear speakers will most of the time only pull the soundstage to the rear which is not we want in a SQ setup.

This post has been edited by GRexer: Jan 10 2012, 05:22 PM