Yes, all three displays are connected as you describe. The ATBD won’t display the OC boot selector from a cold or warm boot when connected as a single display. However, I can successfully navigate that process and boot into Mojave with it as a single display and all ports are visible in System Information and everything works properly. The ATBD does not display anything as a single monitor when booting to Catalina, neither warm nor cold, but I believe it is booting successfully in both cases as I can hear the fans slow down after entering my password. With another display connected via DVI, I can warm boot to Catalina and see the non-ATBD displays, all ATBD ports, FT camera, and audio in System Information and everything except the display works (FT camera, Display Audio, and USB ports). I haven’t tested FW or Ethernet, but they are recognized.
Is there an argument to add in OC for Lilu/WEG that I’m missing? I’ve also been reading the thread that cdf posted and plan to try reflashing the TR card with the DESIGNARE-Z390-NVM33-Elias64Fr.bin firmware. It is currently flashed with TitanRidgeNVM23-E64Fr.bin.