Like Kevin says you don't have RCA audio outputs on your TV. The only audio outputs from your TV are via either Toslink or HDMI. You can either use a DAC (but which must have a Toslink input) or a cheap adaptor (either Toslink to RCA or HDMI to RCA). Many cheap ones on sites such as Amazon or eBay. You then route the RCA output to your preamp to any of its inputs (other than phono/Turntable if it has it).
Not sure why your "optical cable adaptor" did not work. What is it and how did you connect it up?
Current: [P20] Roon/Tidal > Custom PC> Chevron Paradox NDF16 > Phast Pre > Neuro. 686 > Tannoy Berkley (RFC tweaks)