Setup: Laptop --> USBC-HDMI converter --> TV --> HDMI ARC --> Beam Gen 1 (with Era 100 surrounds).
When using a USB-C to 4K60 HDMI Anker Nano hub, I only saw stereo as a supported format (or more precisely linear PCM 2.0). However, I knew my setup can do more.
I used CRU tool to modify the EDID of my Sharp 55'TV HDMI to support 5.1 PCM (lots of other documentation on the web on how to do this so I won't go into the details. It's a matter of downloading some software, ticking some boxes, and restarting windows).
Select 5.1 in Windows speaker configuration, and PCM output format (i.e. 16 bit 44 KHz or similar)
Select Dolby Digital 5.1 (DD 5.1) as an output audio format on my TV, whose ARC (not E-ARC) port is linked to the Beam Gen 1 + Era 100 surrounds. If your Sonos device natively supports linear PCM 5.1, you just need to set it to bypass.
This gave me 5.1 surround from all Windows sources. On my case, My Sharp TV is transcoding any input format (i.e. Atmos in version 1, L-PCM in this version 2) into DD 5.1. Not sure if all TVs can do this - I guess I struck it lucky.
Hope this helps someone!
