2015 and 2016 models support hdmi 2.0 and could be updated to hdmi 2.a via software. Why isn't Pioneer updating these receivers? Spending another 500-600 euros for HDR after just a year usage seems stupid. Please Pioneer update your sh*t.
The video circuitry and processing in the receiver may not be compatible with HDR.
That's why some 4k BD players have two HDMI outputs. One to go directly to the TV for picture and the second to provide uncompressed audio to the receiver.