Well I bought that Crossfire Tek 50.4 and its one clean MoFu with a plenty of power.
All you folks that say rear fill will trash the soundstage, need a better HU! My rig sound so much better with four speakers and a sub than just a front/sub setup.
The system is a 860 hu, Crossfire tek 50.4 Pioneer 510d sub amp, Boston pro's 6.5 in front, Boston 6.5 coax in rear and Pioneer Lo-pro 12" sub in the rear hach(4 Runner). It wont change anytime soon onless something go's boom.