It shouldn't cost much more on a parts basis but the change from the 44s drivers to those on the 99s, 5's, 9s and 11s would require a whole new XO design to go with them, a new tweeter too. The 99's tweeters were subtly hornloaded to keep up sensitivity with the midrange driver. All these could be housed in the 44's cabinet.
Yeah, the DB was really ahead of its time. Back then SETs were the domain of horn and single driver folks and active bass and subwoofers were not as widely accepted as they are today.