Question: Apple TV 4K + Vizio M55-C2, SB4051
This is not a question; just sharing experience of hooking up a new Apple TV 4K with a Vizio 4K TV and a soundbar. I had some issues with the set-up initially because of older cables and not using the optimal connections. Firstly, routing the apple TV >> Sound Bar (SB4051) >>TV(M55-C2) using HDMI cables and the standard HDMI 1 (ARC) input does not work well because that input is only 30Hz for 4K video; therefore use the HDMI 5 input on the TV which supports 60Hz 4K video. However, that input is not ARC (Audio Return Channel) compatible so the best arrangement that I found by experiment is Apple TV >> TV (HDMI 5) and then TV >> Sound Bar using an optical (Toslink) cable or an HDMI cable from TV HDMI 1 to HDMI out on the Sound Bar. This combination gives high quality video and DTS 5.1 surround sound.
If the Apple TV does not select 2160p video automatically, it can be set manually to the 60hz 4K SDR setting; my TV does not appear to support HDR though newer models likely do so.
Apple TV 4K, iOS 11.2.1, WiFi connection to iMac