There is no “headphone amplifier” in the Pro iDSD / Pro iDSD Signature. Just a gain stage/line driver that is sufficiently powerful to drive many headphones directly, however, doing so is clearly a compromise over using a dedicated headphone amplifier like our Pro iCAN/Pro iCAN Signature. It is adequate for anyone occasionally using headphones while mostly using a speaker based system. However, unlike the Pro iCAN/Pro iCAN Signature, it is not optimized for headphone drivers. It cannot drive as wide a range of headphones as the Pro iCAN/Pro iCAN Signature and it lacks the sonic controls offered by the Pro iCAN/Pro iCAN Signature.
It should be seen as a state of the art DAC, which may drive headphones, and not as headphone amplifiers that accidentally had some “normal DAC” fitted.