Newbie setting up Samsung TV with Arc, Sub, Era300s in Xfinity Streaming environment - PCM 2.0 only?

I’m new to Sonos.  Took the dive with theatre completion: Sub4, 2xEra300s.  Now I have 45 days to see if they are worth the $$$.  I’ve deep dived many conversations here, but still cannot achieve Dolby Atmos.  This reminds me if building my Jeep… all the mixed info and dependencies on component and OS providers - ugh - my head hurts.

First Impression:  Adding the sub and surrounds, moving my Arc out from under my TV which may have been blocking drivers and trying to establish Dolby Atmos, but getting from Dolby 2.0 output to Dolby multichannel PCM 2.0 -- the Arc came alive.  Much better, but not good enough to keep the Era300s yet.

My system:
Samsung QN85QN85BDF
- Arc input to HDMI 3 eARC, Sound Output set to same.
- External Devices:  Anynet+ (HDMI CEC) on
- Expert Settings: HDMI-eARC Mode - Auto,  Digital Output - Auto, Dolby Atmos - on, (Pass Thru not active)
Sonos:  Arc, Sub4, Era300 surrounds
Source:  Xfinity Streaming
I’ve tried “The Voice” broadcast in Dolby WAV to allow Atmos, MNF on ESPNHD, Avatar
(I’m not 100% sure my sources are enabling Atmos, but they are my most watched sources which could influence that I don’t need Era300s.)

QUESTION: 
1. What is preventing me from achieving Dolby Atmos:  set-up or source?
2. I am getting almost nothing out of Era300s.  Not worth the $$$ at this point.  Speaker stands arrive tomorrow and I’ll run TruePlay, but for now, the Arc seems to be pushing 98% of experience even with surrounds volume at +8.  When I use the volume slider on the Era300, the Arc increases volume in that zone 5x the Era300.  How do I get more out of the Era300s?  (is it because I haven’t achieved the right source/format yet?)

Thanks in Advance!
CigarXO