Dolby Atmos does not work over optical. This is because digital optical cables do not have the capability to transmit the Dolby Digital Plus or Dolby TrueHD audio codecs, both of which can contain Dolby Atmos audio.
Digital optical cables have a limited bandwidth and can only support up to 5.1 channels of audio. Dolby Atmos, on the other hand, is an immersive audio technology that can support up to 7.1.4 channels, including overhead speakers for a more three-dimensional sound experience.
To transmit Dolby Atmos, you need a connection that can handle the higher bandwidth and audio formats required. HDMI is currently the only method that can support Dolby Atmos, as it has the necessary bandwidth and audio capabilities. HDMI cables can transmit the Dolby Digital Plus or Dolby TrueHD codecs, which are used to deliver Dolby Atmos audio.
I personally encountered this limitation when setting up my home theater system. I initially connected my Blu-ray player to my AV receiver using a digital optical cable, hoping to enjoy Dolby Atmos audio. However, I quickly realized that the sound was not as immersive as I had expected. After some research, I discovered that Dolby Atmos requires an HDMI connection. So, I switched to an HDMI cable, and the difference was remarkable. The overhead sound effects were much more pronounced, creating a more enveloping and realistic audio experience.
To summarize, Dolby Atmos does not work over optical because digital optical cables do not have the necessary bandwidth and audio capabilities to transmit the Dolby Digital Plus or Dolby TrueHD codecs required for Dolby Atmos. HDMI is the only method that can support Dolby Atmos and deliver the immersive audio experience it offers.