Well, going with a DC source saves the huge expense of an Autoformer. What's going on special between the battery and the amp ? Any isolation ? Also Dan, are you using anything special as a power supply to the MacMini ,as in noise reduction ? I've not used a computer or drive source yet, but they do have that switching power input that I'm told is the largest source of noise. Anyway, I've auditioned and have the dBAudio USB Tranquility Dac and it is special, very special. The guys can argue points all day long, for ripped source music, it is in a class of it's own. I couldn't believe it !!