I have a Q60 65” with the Arc. 
 

Netflix app won’t show Dolby Atmos symbols until you start Amazon Prime app, then enter into advanced picture setting to set DD+ again. After you did that, Netflix will be able to stream Dolby Atmos DD+. Sonos app will confirm that. 
 

Amazon Prime app doesn’t show the Atmos symbol somehow. There are two versions of Jack Ryan on Prime. Both of them shows 5.1 but one of them actually stream Dolby Atmos DD+ when you play it (even though it indicates 5.1 in the description). But I can’t find other contents there with Atmos so far. 

Oh, the last bit. 
 

The Atmos effect is very very subtle. Not worth the trouble in my view. The stereo soundstage has been reported as amazing, but in my comparison with the Playbar in the same spot, it is not that much of an improvement. Playbar comparing to the Beam was a hugh step up for me though. 
 

I have only used the Arc and Playbar with the Sub and One surrounds. 

Amazing.thanks @ekwok  

I have the beam + 2 rear ones . In music its excellent but in movies I find the depth is struggling . I purchased the sub recently (awaiting delivery) hoping it will enhance viewing experience but I'm wondering if it would be better to instead of sub replace the beam with arc 

Beam+Sub+LR+RR vs Arc+LR+RR

I would go for the Arc setup. Beam’s sound stage is too narrow even with the surround rears. Huge difference from that of the Arc. If it is to compare to Playbar+Sub+LR+RR, then it is not so clear cut for me. 

I found this device that allows for FULL Atmos over Dolby TrueHD to be passed to Sonos Arc and passthrough full video to TV.  Let’s you keep you existing non eArc TV and ALSO get full Atmos on Sonos Arc!!

Arcana by HDFury: https://hdfury.com/product/4k-arcana-18gbps/

Device separates out full audio (up to Dolby Atmos over Dolby TrueHD) from any external HDMI source and sends it to the Sonos Arc while also passthrough full 4k video (up to 18gbps) to TV!  They are accepting pre orders now.