OK with RCA cable
Finally I was able to replace the 25ft optical cable with an RCA.
It works ... I get sound from the reception of the digital antenna to the TV to the Denon. I need to play with the sound settings, as Pepe7 suggested, because right now the sound quality is not worth all the trouble I have gone through, since sound only comes out of 2 speakers.
I was not able to test if a shorter optical cable would do the trick. Maybe one day I will get to do that just in the name of R. Proffitt and of course, of this great Forum
Thank you all very much for you help!