I don’t believe that either option will work as a result of the HDMI version in use in the HD621.

Personally I use an SPDIF connection for Netflix. It’s far from perfect, but an acceptable solution.
The most viable option I’ve seen is to buy a UHD BD player with two HDMI outputs that has similar streaming options.

861v4/ID40/LPS, HD621, Roon, BAT VK-600se, Impulse Ta'us. Director/Heed Canamp with HD600s.