Pioneer 4-Channel Class D Amplifier Black GM-DX874 - Best Buy
Amazon.com: Kenwood X302-4 eXcelon 50 Watts x 4 4-Channel Class D Amplifier : Electronics
Amazon.com: Massive Audio Blade BP1000.4 Car Stereo Amplifier. 4 Channel Amplifier 1000 Watts, Class A/B, 2 Ohm Stable, with Bass Boost. The Best 4- Channel Car Amplifier with Built-in OEM Line Converter :