I have a UE43RU7100KXXU and have just recently purchased a Sonos Beam sound bar that all works great together in normal PCM sound quality with my Sky Q and XBOX ONE in HDMI 1 and 2 respectively and then the Sonos in HDMI 3 (ARC), The problem is when trying to play in Dolby Digital on my soundbar, i get a terrible audio lag (500ms Roughly) which cant be adjusted for as the audio delay option only allows you to increase this lag. I have proven the problem is with the pass-through within the Samsung TV, as when i plug either the Xbox or Sky directly into the soundbar i do not have this problem. However i am not prepared to keep unplugging wires in order to achieve this as i often use apps on the TV as well as both my SKY Q and Xbox. Surely this can be fixed with a software update, as from your forums i can see this is a common problem.
Summed up nicely and reflects crux of the issue with the TV and similar in my situation (with Q80 TV + Q80 Soundbar) and shown by others as reflected accross this forum and the soundbar one.
I have resorted in my situation routing to soundbar first with Cable Box and with the PS4 HDMI to TV but optical audio to soundbar. This causes other issues as I have to effectively disable ARC (through turning off HDMI-CEC), but then need to switch back on again if I want sound back down to the soundbar from the TV apps (iPlayer / Prime etc) so is a headache.
In short, this shouldn't be such an issue in this day an age :-(
Samsung is there a solution?
There is alot of forums with people venting the same frustration...
These are just a handfull of forums, there are many more if you keep searching
Please do something