Just received my amplifier today and i am just downright impressed by this amp. The size of the 4000.4 is just amazing considering how much power it produces. Hooked it up to some infinity 6x9's and pioneer 4x6's and thought i was going to blow them! The sound was crystal clear, got insanely loud, and sounded a ton better than my old Hifonics 4ch. Another great addition is the 0 gauge power and ground adapters. Great to give this power hungry amp the power it needs. Was skeptical at first because i never bought anything Polk but in the end NO REGRETS at all! If 50 watts rms is not enough for your speakers, upgrade to this amp just be sure you have quality speakers.