Back when I had a very old tv and wanted to hook up my dvd player to it, but couldn't as it didn't have the right connectors, I used something called RF modulator that I got from radio shack, back when radio shack was still a thing. I don't know if it would help you, if it has all the right connections that are needed for your sound system, it's something you'd have to check.
How to hook up older Memorex tv without antenna to a Dolby digital plus box
Exactly what TV, what connections are on it, and what are you connecting it to? Dolby Digital is a technology for sound processing, it's not something you hook up a TV to. Is this a cable box, DVD player, what?