CH3/CH4 as audio output: 4 groups of speaker sockets can connect to 2 pair of speakers. Besides connect to active speakers, CH3/CH4 also can connect to another M4 amplifier to connect more speakers, in this way multiple amplifiers and multiple speakers can be connected in turn, to achieve one audio signal be shared in several rooms.
CH3/CH4 as audio input: one input corresponds to one output (ex. CH1 speaker socket will output the audio signal that CH1 inputs), which means that two groups of stereo audio signal (or 4 groups of mono audio signal) can be input at the same time.