The IMR-4 connects a TV, VCR, CD player, vhf radio, DVD or portable mp3 to your marine audio center with expansion port. It provides output for an external subwoofer or loudspeakers, and a separate audio zone with independent volume. Output of a head phone connection is also available. External booster required. All inputs and outputs are stereo (Left + Right). The Auxiliary input channels can be configured to accept line level, or high level (power amplifier output) signals. Differential input circuits are used to minimize interference, and to avoid grounding for connections from bridged mode amplifiers.