The amp is spec'd at 1 volt. Measuring it at 2 volts is in keeping with measurements of other headphone amps, but expecting it to meet the published specs at 2 volts is somewhat of an unreasonable expectation.
Have any blind listening tests been done to see if anyone can actually hear a difference between this amp and say a Benchmark or TOTL Topping headphone amp? Audio equipment is made for listening - beyond a certain point measurements are meaningless. I'd like to know if there is any audible difference between a 101 dB SINAD and an 83 dB SINAD in actual listening practice.
At any rate, this amp is overpriced. It's likely handmade, more or less, in the USA by people paid at a local wage scale, and in small numbers - so I can understand that it is going to cost more than an amp made mostly by machines in Asia and with just a little poorly-paid human labor; still the cost is unreasonable. Perhaps the value of a product like this is it shows there really isn't a demonstrable correlation between price and performance in audio gear.
It's also interesting to point out that Schiit products are assembled entirely in the USA and they have much lower prices and better performance. I'm not sure I could hear the difference in performance, but I can afford to BUY a Schiit amp-