Been meaning to post for a while now, we played around with our set up and manage to find something that suits whilst maintaining Dolby Atmos.
We have an LG tv and the HW-N850. When we first set the sound bar up we would have a terrible audio lag, mainly on netflix. Normal TV and Amazon were much closer. This was really bad when on a WIFI connection, so we switched to HDMI which made it closer, but definately not right. We read somehwere about the TV not being fast enough at processing Dolby Atmos, so it essentially processed the visual faster whilst the audio was processed slower and then needed to be sent to a different device.
We switched this over by bying a Roku 4k streaming stick (one build to stream Dolby atmos). Our current set up now relies on the Roku being powered from the TV but going into the HDMI In on the sounbar. We then run a HDMI from the soundbar into the TV. For us this has fixed the issue, although it means we not have a streaming device managing all of our apps rather than the smart TV functions.
When you say you're running HDMI to the soundbar, do you mean HDMI ARC?
Unfortunately, I have a TCL Roku TV - I suppose I could add a Roku stick to see if that works but... I was able to "downgrade" to Dolby (in the TV settings) and the sound and video sync up better but, of course the point is to be able to use Dolby Atmos.
Samsung seems unwilling to admit this is an issue with the TV and not the external equipment. I bought a UN65NU800 a couple of weeks ago. Unplugged the 54" Panasonic plasma, which has worked fine for 7 years, and plugged the Samsung into the same cables I'd been using. Basically power, HDMI in, and optical sound out to a Panasonic amp. Audio delay is all over the place. It varies by channel and time of day...or something. There are times when things are in sync and times when they're way out, with no apparent pattern to it. Setting the delay time in the TV setup doesn't work, because the delay varies so much. It doesn't make any difference what decoding I set for the amp, including none. Sound out of the TV speakers is in sync. The fact that the only change made was the TV tells me the issue is there. Hopefully, they'll identify some sort of software fix and update it one of these days.
I have N850 and 65Q7F and the audio sync issue was driving me mad. As you say, samsung are useless and just read from screens and dont know the products. I found that connecting my virgin V6 box to the soundbar and using the ARC from tv to N850 the sound problem was solved. Only problem is the limited connections on the soundbar. I dont have a problem with my DVD player connected to the tv one connect box. I sometimes have issues with av inputs randomly switching the DVD on and then a pain getting back to the correct input.
I've recently purchased the 55" Q9FN and the HW-N850. I've connected via ARC, however having the same audio sync issues where I need to almost remove delay as opposed to add (which is my only option!). I've purchased a new highspeed HDMI cable (as the current one is pretty old) to see if that helps. If not I'll connect my SkyQ box directly into the Soundbar itself in hope. The problem I'm worried about is my Xbox One X and PS4 (which I've yet to try).
If I get no joy and everything is still out of sync then I'm tempted to just send the soundbar back and live with the TV and diminished audio. Things like this really grate on me and I don't have time trying to search for every option under the sun when other customers are already having the same issues with no joy.