Some 5.5 million households added a high-definition television set to their furnishings for the first time during the period from last year's holiday season to this year's Super Bowl, according to a study conducted by Frank N. Magid Associates. Another three million added a second HDTV set to their homes during the same period. The Marion, Iowa-based research group estimates that 28 million homes now have at least one HDTV set -- or 25 percent of all U.S. households. Virtually all of the sets receive TV signals via cable or satellite companies; only 3 percent say they receive programming over the air. A significant number of HDTV set owners -- 30 percent -- said that they do not get HDTV programming at all, citing added charges by cable and satellite providers.