At most your getting 1080i, check, and you have too run audio seprately on both, check.
But I would call the cable comp to see if you can get a new box free, DVI has not been used for some years now. A new box could maybe give a little better PQ.
need some help. just purchased samsung ht-z520. the unit supports 1 hdmi in. my cox cable box only has dvi out. currently i have the composite cables running from my cable box directly to the tv. can i run the dvi out of my cable box into the hts HDMI IMPUT? CURRENTLY I HAVE THE DIG. AUDIO OUT FROM THE CABLE BOX TO THE HTS. IS THERE ANY ADVANTAGE TO RUNNING THE DVI FROM THE CABLE BOX TO THE HTS VS THE COMPOSITE STRAIGHT TO THE TV? ANY HELP WOULD BE APPRECIATED.