Its very common for a 4 chnl amp to have a 2 chnl/4chnl mode switch. In 2-chnl, only thr front L/R RCA inputs need to be populated for all 4 chnls to play. In 4-chnl model, all 4 RCA inputs need to be populated. So no Y cables needed. However, some amp do not have this switch and ALL RCA inputs need to be populated, So in a case where you only have a front and rear RCA output from the media unit, then Y cables are needed when two amps/zones are needed.