I just remembered that my £20 Tesco (Technika) DVD player claims to play
HDCDs.
The setup menu has 3 settings for HDCD: OFF, X1 and X2.
There was of course no documentation to explain what these settings do.
I guess that X1 and X2 control the headroom extension feature.
If I could find which of my discs have headroom extension enabled ...

--
Eiron.