Nothing is going to recoup all the losses that digital cable channels sustained by being forced into a composite cable. But any analog channels might well come out better via composite compared with via component video or even HDMI from a different more sophisticated cable box.
It depends on what kind of comb filter your TV used for composite inputs versus what kind of comb fiter any "improved" cable box may have to make analog channels come out as other than composite.
Upscaling receivers also need comb filters to make composite source cross feed to the S-video output or the HDMI output, etc. There is no guarantee this comb filter will be better than that in the TV either.
You will want to plug the DVD player into the TV using component or HDMI even if the cable box is connected to a different TV input using composite.
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