^ The above statement (and bolding, and exclamation mark) comes across like you're trying to save humanity from making the huge error of considering the NH's as a primary headphones. That's why people didn't approve of your post. The NH's are awesome primary headphones for many people. At least the above comes across more like an opinion rather than a mandate.
1) What you are hearing with the ZuperDAC and the adapter seems to make sense. 2) The ZuperDAC does have an amp btw (ESS Sabre ES9601) 3) I have no idea why the DF 1.2 and adaptor is not behaving the same way. It might have to do with differences in the amp chip (output power?) or the output impedance, but I really don't know.