To have used balanced outputs with a bus-powered device would have severely increased power consumption and consequently reduced the battery life of the computer. It is important to note that there is no sonic difference between balanced and unbalanced outputs. The only differences are level and cable length. Since the vast majority of Duet users have powered speakers and aren't making 1000' cable runs from front-of-house to the stage at Wembley Stadium, the application of unbalanced outputs on Duet is not only totally sensible, it's also more flexible.