I really need just some confirmation here as Samsung Support has told me both yes and no.
I have a MU8000 and a N850 with Dolby Atmos Soundbar. I have the soundbar connected to the TV via ARC and my Xbox, Ps4 and Sky Q box connected directly to the TV.
Will this support Dolby Atmos or does the devices need to be connected to the soundbar directly? Samsung have said it doesnt but i am not sure.
Samsung only support Dolby digital+ on arc. From what I gather you will need earc which is part of the HDMI 2.1 Some devices can be updated to earc but at the moment no one seems to know. So to answer your questions you need to connect directly to the sound bar with all the devices if you want atmos. All depends how many HDMI connections on your sound bar.
I have a dennon av receiver and have to connect my shield TV direct to that to get atmos. If I use the arc I get DD+. Also noted on the latest windows 10 that it will pass through bitstream atmos now, via HDMI, which is great for Netflix which both the Samsung and shield do not support.