This is really good to know.

Do you know for Apple TV and 4K Box TV (equivalent Sky 4K Box) what resolution we require to have 4K on a TV?

To be honest if the HD Fury resolves the 4K issue of the HD621 that would avoid me having to buy a UHD722.

G65, 598DP, UHD722, DSP5200SE Front LR&C, Cable TV, Pioneer Kuro LX509