Hi Regeli,

Thanks for the info!
I thought that the Apple TV 4K always outputs LPCM if you set audio structure to automatic?
So it decodes for instanance Atmos soundtracks from iTunes to LPCM which your HD621 can process.
But iTunes or Netflix Atmos of course is DD+ Atmos, unlike UHD blu-ray’s ‘real’ high-res Atmos.

Regards,
Bob

861v4/ID40/LPSU, G55, HD621, 504
Wilson Benesch Square Five front, Square Centre & Square Two rear, Velodyne SPL-1200 Ultra
Mac mini, QNAP TS-219P II, Apple TV 4K, Marantz UD8004, Pioneer Kuro 500M isf
NBS Monitor IV cables