Well the original idea was you could go somewhere, and take easily portable entertainment with you: Music, radio or even watch a broadcast ball-game. It was never the device of choice for sitting around watching cable.
The TV signals it uses are no longer transmitted, and the need for a separate signal source outputting composite video (and maybe a modulator if you don't want to mod the boombox for a composite video input) removes the easy portability advantage.
Modding it to add an Android device is the nearest you'll get to its original functionality, if there's a livestream of the events you want to watch.
Of course its a very niche concept, and I personally would rather use a phone or tablet + good bluetooth speakers, and sell the boombox to a collector who will value it in orginal condition.