As a Zdac owner, I certainly would not consider it a Mid-Fi DAC. Although the price may reflect Mid-Fi status, the SQ is pretty damn good. Put against my Buffalo II the winner to my ear is the Buffalo, but that's more about neutrality than detail. The Zdac has a slightly warmer presentation, but that could be a positive in many situations. IMO there are a lot of "lower cost" DACs blurring the Hi-Fi line today.
That said, the Ayre QB-9 is one of the best DACs I've heard.