Bmdduck,
The things that impress me most about the ZDAC are how clean it is, i.e., no digital hash at all that I can hear, how nicely extended it is from top to bottom, and how much more of the recording I'm hearing than before. I hear more of the reverbs on vocals, tremolo and other effects on guitars, and even subtle lines from instruments I had not noticed in the past. I'm also getting more of a sense of the dynamic range on the recording, maybe because (again) it's just very quiet and clean. I have to add, it's not completely broken in yet, nor have I tried anything but the stock power cord and USB cables that came with the unit. Some have said it gets better with better cables. That'd be cool, too. Good luck.
Jon