I purchased an adequate length of Belden 9259 on eBay and the RCA's from Parts Express
Gold Male RCA's https://www.parts-express.com/neutrik-rean-nys352g-rca-plug-connector-gold--092-112
Nickel Male RCA's https://www.parts-express.com/neutrik-rean-nys352-rca-plug-connector-nickel--092-110
These Neutrik connectors worked very well but require soldering. Avoid crimp types. Match the metals at each end to your amplifiers Female RCA's and your Preamps RCA's
Gold Male RCA's https://www.parts-express.com/neutrik-rean-nys352g-rca-plug-connector-gold--092-112
Nickel Male RCA's https://www.parts-express.com/neutrik-rean-nys352-rca-plug-connector-nickel--092-110
These Neutrik connectors worked very well but require soldering. Avoid crimp types. Match the metals at each end to your amplifiers Female RCA's and your Preamps RCA's