Try the forceraw build with Adjust Display Refresh Rate disabled and Allow Passthrough enabled. I found that this setup worked better on the Fire TV Stick 4K with my Denon receiver and Sony TV.
TV: Sony XBR-65X950G A/V Receiver: Denon AVR-X3600H (Atmos 5.2.4) UHD: Panasonic DP-UB820 BD: Sony BDP-S6200 (Region Free)
Media Players: 2019 Nvidia SHIELD TV Pro, 2015 Nvidia SHIELD TV, Amazon Fire TV Stick 4K Max, S905X3 CoreELEC Device