Hi @artshotwell.
Thanks for reaching out and for your detailed post, let me help and try to figure this out.
Sonos Arc supports the playback of Dolby Atmos audio via Dolby Digital Plus or Dolby TrueHD. Sonos Arc must be connected to HDMI ARC or HDMI eARC to play any Dolby Atmos content. You can find more information on playing Atmos audio through Arc in our Dolby Atmos article.
Most Dolby Atmos audio can be played through HDMI-ARC using the Dolby Digital Plus codec (DD+). HDMI-eARC is required to play lossless Dolby Atmos audio using the Dolby TrueHD codec.
Upon checking the specs of your Samsung Q70R 2019 TV, it says that it supports Dolby audio, here is the link for reference:
https://www.samsung.com/us/televisions-home-theater/tvs/qled-4k-tvs/65--class-q70-qled-smart-4k-uhd-tv--2019--qn65q70rafxza/#specs
You may also verify and check this information directly from the TV manufacturer if it supports Dolby Atmos.
To sum it up, every ingredient in your home theater setup has to support Dolby Atmos, to get Dolby Atmos on Sonos Arc.
If you have any other questions or run into any issues, please do not hesitate to reach out, we’re always here to help.