For budget sq systems I've always just went three way active and bought the raw drivers from parts express. Most mobile components just aren't made for true sq, but for an over bearing high end and something to match up with a very over pronounced low end. Not that there's anything wrong with that, but a pair of Dayton refs and vifa xt25s will smash anything in the car audio realm for the price. Amps like the PPI phantom 900.4 can handle the 3way active for you, or 3 way old school quality xovers can be had for cheap on eBay.
Bought from - Hazardous0388 (4 db Drive 2000.1s), Psychoacoustics (4 Powerbass XA 3000'ds), and blackedoutavy (PPI A200)
Sold to - D-Rew (Knu 1/0), d77543020 (Knu 1/0), F1McLarenAGR (Audioque 4x90), and SacTownBully84 (Knu 1/0)
Traded with - SacTownBully84 (my xa3kd for his xa1.5kd + cash)