4 channel 

Focal Auditor AP-4340 4-ch amplifier

The AP-4340 4-channel class AB amplifier can be used in three modes: 4, 3 or 2-channel.

JL AUDIO JX-400.4D

BLAM Relax RA 804D 4ch amplifier

Ultra-compact 4/3/2-channel D Class amplifier Compatible with OEM head units High-level inputs with auto-turn on

Focal FPX 4.800 4-ch amplifier

Compact 4 channel car audio amplifier. Manufacturer site Worldwide delivery

Focal FPX 4.400 SQ

Compact 4 channel car audio amplifier. Manufacturer site Worldwide delivery

JL AUDIO XD400/4V2