Congrats on your Oppo 105! One of the advantages of the ESS Sabre DAC chip is how it handles S/PDIF. The ES9018 DAC chip does not handle SPDIF like most SPDF receivers do; it does not rely totally on the embedded clock in the S/PDIF signal. It handles it far better and asynchronously. And don't fear 32 bit volume control. My pre doesn't have a remote so I use my DAC to control digital volume. No harm to SQ, at all. Now 16 bit volume would be a different story.
The ESS white paper is an interesting read. Section III deals with the S/PDIF interface.