As I understand (and please let someone correct me if i’m wrong) it with eARC you’ll get full Dolby TrueHD Atmos - on a soundbar (not a full 7.1 system) and only from sources that support it (only Blu-ray's for now as I understand it). Streaming sources only do compressed Atmos via DD+ for which HDMI-ARC is fine. Check with your supplier if the TV supplies the Arc with DD+.

Thanks for your response I appreciate it!  So when using regular tv and or a streaming service such as Netflix, there will be no difference in sound quality? 

If buying a new tv now, I would absolutely, definitely get one with earc as it should save you a ton of potential compatibility issues down the road. 

But to answer your question, I am not sure if a non earc tv can pass dolby atmos to the Arc, it is my understanding that no, it will only be able to pass dolby core without the additional atmos data, but I haven’t checked this as earc is an absolute requirement to me for other reasons.

No, that’s incorrect. HDMI ARC can carry Atmos, in the form of Dolby Digital Plus. Atmos via TrueHD does require eARC. 

Right, apparently there are two different specs within regular arc too, which is why it sometimes works and sometimes doesn’t. In my setup, it doesn’t.

(Ref: https://community.cedia.net/blogs/david-meyer/2018/06/25/dolby-atmos-over-hdmi-arc) 

The Beam and Amp use Single Mode ARC, the Arc will use Common Mode ARC, or eARC. Not sure what issue your setup is having with Single Mode ARC working, but at this moment, unless you’re in a special double secret hardware beta, or perhaps Press, there is no Sonos device on which to test Common Mode ARC or eARC.

Over ARC in general, not specifically talking about Sonos, as, indeed, I don’t have a Sonos device compatible with Atmos, though I am eager to get one if one matching my requirements is ever released.

I think one of the potentially most useful benefits of eARC is it forces correct lip sync, something that wasn’t mandatory with ARC. Given how many people have had issues I really hope manufacturers get this right as ARC was open to a lot of interpretation. We’re I buying a new TV I’d only look at eARC models as it’s going to be the standard going forward for audio formats too.

My 2c: Don’t bother buying a new TV without eARC. When I bought my new TV last year I thought I carefully specced out its features (4K, HDR10 etc) and the only thing I considered missing was Dolby Vision. Sadly it also lacked HDMI 2.1 which meant no eARC for me.

Earlier this year I needed a new TV at work (I work on Xbox) so I asked a buddy on the HDMI team for a recommendation, and he said LG C9 which has the most complete feature set. So that is on my office wall now, though sadly I haven’t been able to actually be there for two months. I should have asked for his advice when I bought my own TV last year.