I came across this from a review of the Henry Audio USB DAC 128 Mk 2. (http://www.6moons.com/audioreviews2/henry/1.html)
In your first iterations of the DAC, you employed an ESS Sabre chip. The new DAC has gone with a different chip. Why? "...what made me choose another chip was the discovery of an internal math bug in the ES9022/9023. A >-1.3dB full-scale square wave played through their chip will generate great amounts of distortion. With modern compressed music, that isn't just a theoretical occurrence. I worked many years with signal conditioning and was able to see what goes on. In technical terms, the internal FIR filter does a 2's complement overflow where a very positive number actually flips around and becomes a very negative number. This occurs before the sigma-delta modulator. A digital limiter or lower gain in the FIR would solve this."
DAC's may have software bugs which compromise the sound! One may say this is unforgivable - after all, the math in digital music has to be the one thing you CAN get absolutely correct. But then again, we're talking about real-world products made with money and time constraints, and open to human error.
Ultimately, no matter what the specs might indicate as being "perfect", the final test has to be via our ears. Trust your ears!
But, if it sounds good to YOU, that’s what counts. (Steve Hoffman)