The one requirement on the transport is that the output bitstream be an exact copy of the data on the disc.
Some transports (Wadia 270, and at least one ML model I can't remember) perform resolution enhancement by dithering the orginal data on the disc to generate a new bitstream with more bits per sample (24 in the Wadia's case).
On these transports resolution enhancement must be switched off to retain the HDCD encoding in the output bitstream.
Similarly any resolution enhancing digital processor (Genesis Digital Lens, AA DTI Pro family, etc) in the signal chain must have enhancement turned off.
Some transports (Wadia 270, and at least one ML model I can't remember) perform resolution enhancement by dithering the orginal data on the disc to generate a new bitstream with more bits per sample (24 in the Wadia's case).
On these transports resolution enhancement must be switched off to retain the HDCD encoding in the output bitstream.
Similarly any resolution enhancing digital processor (Genesis Digital Lens, AA DTI Pro family, etc) in the signal chain must have enhancement turned off.