Someone here contacted HDFury who evidently said there isn’t a device anywhere at present which can extract full resolution audio from HDMI and re-embed it onto HDMI-eARC, which is what would be required for full TV bypass to Arc.
There was a suggestion that they might be considering making such a device. Timescales TBC.
Been emailing with HD Fury, this is the latest:
yes we already made it work in our labs, later today we will show proof of concept video on our discord server > channel: straight from the labs.
Feeding Sonos with Atmos from ATV4K
Hdfury has got it to work and shown concept video today.
We all need to voice demand to them so they can speed up production based on demand
https://www.hdfury.com/contact/
Thanks in advance
German company FeinTech stated something similar. They are also considering developing a product for this use-case since there are so many requests from the German Sonos Community.