Monoprice Onix Series Digital Coaxial Audio/Video RCA Subwoofer CL2 Rated Cable, RG-6/U 75-ohm 6ft - Monoprice.com
Subwoofer adapter | AV-Connection
ATAUDIO HIFI Single RCA to Dual RCA Subwoofer audio cable Pure Copper One Sub-2 Splitter Y RCA Cable - AliExpress
Amazon.com: Mediabridge™ Ultra Series RCA Y-Adapter (8 Feet) - 1-Male to 2-Male for Digital Audio or Subwoofer - Dual Shielded with RCA to RCA Gold-Plated Connectors - Black - (Part# CYA-1M2M-8B) :