Your Sony is newer than mine, so if in theory i can get Dolby Digital Plus via ARC and thus a lossy version of Atmos then in theory you should be able to as well. So i'd say yes, audio wise you would be losing out using Optical over HDMI Arc.
thanks both, if I do I need to decide what to ‘lose.’ The PS4 pro is more an issue as it won’t output 4K unless hooked up to hdmi 2 or 3, one of which is the arc.The following is not supported via optical - 5.1/7.1 multi-channel PCM, Dolby Digital Plus, Dolby TrueHD, Dolby Atmos, DTS-HD Master Audio, DTS:X, and Auro 3D Audio.
You will also lose the CEC-HDMI function.
But you will get - two-channel stereo PCM, Dolby Digital/Dolby Digital EX, DTS Digital Surround, and DTS ES.