CONCLUSION
A DAC is far more than merely the sum of its parts. There's no shortage of new releases using all the latest chips and packing all the latest buzzwords. But that doesn't mean they compete with the real deal---there's just no substitute for proper design and implementation. Making purchasing decisions based purely on chips and specs has a good chance of leaving a person disappointed. The Parasound Zdac is a great example of this, it doesn't use a cutting edge DAC chip or USB receiver, yet it manages to transcend the limits of what I expect from the average $500 DAC.
In summary, the Zdac looks, feels, and sounds like it could be a $1000 unit. It certainly didn't feel out of place in my rack with numerous competitors in that range. As a DAC, the Zdac offers exemplary performance with practically zero downside unless we count the lack of support for sample rates above 96kHz. As a headphone amp it could use a few tweaks, but still manages to sound excellent with the right headphones. Do I recommend it? Yes! Rather strongly at that.