Right now I have: Male RCA to Female Aux -> audio source Male RCA to Piggy Back Cable -> speaker amp/speakers Female Coupler to Male RCA cable -> Subwoofer This has run fine for years.

They're also pretty expensive: $15 for either the 1/8" to RCA or 1/8" to optical adapter, neither of which is very long (though they don't need to be).

A plug and socket for coaxial cable. RCA connectors are used for analog audio signals (see analog audio). They are also used for digital audio (see S/PDIF) and analog video (see composite video ...