You can extract eARC audio and send to HD621 using something like this:
VAX01202 HDMI eARC Audio Extractor & Splitter.
However, bear in mind that what the TV sends to it will depend on the EDID of the HDMI sockets on the TV, which might be a problem if you are using LPCM in 5.1 (or above) as not all TV's like accepting this (my old Hisense OLED as an example).
The box described (and others like it, as there are a few!) means that you can use your TV as a switcher for all your sources, the downside is that the TV has to be powered up to do this!
Paul.