8K HDR hardware

Hi, I try to transcode ProRes 4444 8K HDR10 to h265 - but after select high10 Hardware acceleration switch to Software. What GPU needed for HW transcode o High10?

my HW:

Asus X99-E WS

i7-6950

96Gb RAM

1GPU 1080Ti

2GPU 1080Ti

10Gbe

Also i have 3GPU - 1080Ti but not imstalled