Don’t connect the DVD to the STB. It will connect directly to the TV. There are multiple ways. If you use the same type of wires like the cable box you will have Green/blue/red for video and red/white for sound. They will be component or colorstream input on TV. That will be the best picture.
You can also use composites which are Yellow for video and red/white for sound. That will be normally be AV input on your TV.
Last way would be coax wire. It will say RF out on the DVD and that will connect to the screw part on the TV. That will be on the TV input on either channel 3 or 4.