I do not agree that determines if a unit has a black background as there are other factors but just for the h. . . of it.
DX90, headphone out into my fi.Q DX90 all the way up, turned the fi.Q all the way up, with both on high gain. Now that goes way above what has been asked for. No detectible hiss. To be honest, with this extreme amplification of the signal with no music, I would get some level of hiss. None.
Now for more impressions and reviews please.