What makes a DAC so expensive?

A:  My friend just died of a stroke

B:  But his body temp was exactly 98.6 - he was healthy

A:  He smoked like a chimney and ate bacon every meal

B:  But his blood pressure was exactly at the mid point of normal range for his age and weight

A:  Are you an idiot - he is dead

B:  I believe based on my measurements he is still alive

A:  Dumb ass

Power supply noise will show when THD+N is measured. There could be a lousy power supply which would be audible. All DACs will have noise from a power supply but do they effectively deal with it. If a DAC is audibly transparent , distortion and noise is below the threshold of human hearing, I'm not sure I understand the point. 

No audio equipment is 100% transparent to the human ear, not the recording studio equipment, and not the playback equipment.

I just bought the RME adi-2 FS DAC and it is awesome.   For me it checked all the boxes, great sound.... unbelievable feature set,  made in Germany,  full function remote, and most importantly at the price where I felt it made sense because let's face it, digital technology moves fast.  It easily bests my NAD M51 which is no slouch and was twice as much 7 years ago.   So for me this was the best bang for the buck.    

the dcs stack is incredibly good