@Not_very_fast: 1) If you have connected the digital audio cable from the TV to the receiver DTV/CBL optical input jack, after turning on TV and receiver, are you selecting DTV/CBL as input source button on the remote control to connect to that digital audio input on the receiver? 2) If that doesn't work, try connecting the receiver end of the digital optical cable to the CD optical digital input on the receiver and select the CD source button on the remote control? 3) If neither works, when you unplug the digital optical cable at the receiver end and look into it, do you see (red) light? Sometimes there is a tiny cap covering the center conductor through which the light is transmitted on both ends of the optical digital cable, which must be removed at both ends before inserting the digital optical cable into the TV and receiver jacks.
Also in the TV menu, you are correct that 'Search for CEC devices' and 'Auto-detect' have no meaning except for HDMI connections (not for S/PDIF), so a coaxial digital or optical digital connection will not be auto-detected and will not be searched for. In the TV menu, Settings, Audio, S/PDIF and ARC, are you selecting something other than 'Auto-detect'- suggest trying PCM-stereo or DD and then see if you get sound through the receiver when selecting DTV/CBL or CD input source (depending upon which optical input jack on the receiver you have connected the digital audio cable to). It should work.