This is what I’ve done at the end in case it was useful for somebody landing here in the future.
- Connect the Vero4k+ directly to the display via HDMI.
- Connect the Vero4k+ to the AVR using a TOSLINK cable.
- Mute HDMI audio output (display settings) on the Vero4k+.
- Enable DD and DTS pass-though.
- Enable AC3 transcoding (see guide).