Hello, sifu's wanna ask about how to use the RCA behind the head unit? I want to add an extra pair of speakers to my car but I don't want to add an extra amplifier is it possible to utilize the RCA port behind to wire the extra speakers? What type of cable I need for this installation. Sifu please advice.

That was Low Output for external equipment like pre-amp, active xover, amplifier, DAC & etc.. If you plan to run without amplifier just connect to existing factory speaker cable/wire..