I'm using a G68, HD621 and an ATV3. Works like a charm on HDMI to HD621.

Assuming a local HH can square you away.
If not, I would be happy to update your config files (comparing to mine), assuming you still have them and would be comfortable doing your own uploads.

Meridian G68 AXV, HD621 | Cinepro 2k6mk5 | 4x Scanspeak A4 monitors, center & 26W Sub | RPi Hifiberry digi+ | Roon