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From information that I see online for that Kenwood, including the photo below, it does have one optical input. Did you mean that you are already using that optical input and don't have one free, or perhaps you didn't see it there? That optical input would be the best choice for running audio from the TV to the receiver because it will give better quality and allows for surround sound.
If you do need to use the analog RCA connections, then you probably need to turn the speakers on the TV off (likely in the audio menu on the TV) in order for sound to come out of those jacks to your receiver.