Convert your PC or notebook stereo speaker port (3.5mm jack) into regular RCA and connect it to your stereo system. Most cellphones and other mobile devices also uses a 3.5mm jack output and can use this cable to connect to RCA audio system.

If having multiple 3.5mm jack outputs on PC sound card use more cables to ensure Front Left/Right, Centre/Subwoofer and Rear Left/Right can be connected to analogue surround sound amplifier or receiver.