My AVR does not offer me to upgrade to 3.90.50.00. It says 3.90.35.00 is the latest version. Did you use upgrade from AVR or some kind of manual upgrade? Is there a possibility to downgrade?
It was not manual but an offered OTA upgrade, firmware has changed from 5400-9380-4472 to 5200-2411-4413.
Final results:
No problems with Q5pro DTS-HDHR on the old 1911.
God damn you, Denon, you blew it!
Not that the Denon X3200W (with new DTS version 3.90.50.00) does not handle DTS-HDHR. It still works from the old NeoTV media player, the Blu-ray disc player, and the UltraHD disc player. But not with the Q5pro, or the laptop anymore (VLC3, Kodi Leia, Fab Player 5).
I can only warn people, don't buy a new Denon AVR, or upgrade the firmware, until this nasty bug has been fixed. Maybe it's not a bug at all but intention.