If you mean 4k game, the latency will be too long, what else?
For Netflix 4k, I think you could directly connect to your HD621.


HT: Audiocom LX800CE, MP-60,HOLO MAY*2 Analogue speaker(LRC), DSP5200SL (side), DSP7200SE (rear),AntimodeX4,JTR Cap4000ULF*2,Christie HD8C,GIK Bass Traps.