@Saturn94 – Thanks for this.
From my quite limited understanding, there seem to be two parts to the puzzle. First, whether PCs can transmit DSD over HDMI. Wrt to that there is, for instance, this:
And the second part is whether an Oppo as an endpoint can accept DSD over HDMI. From what I’ve been seeing it seems like most information on the interwebs (and of course your experience, and the Oppo manual) says that this is not possible. But then there are some reports (e.g., here: https://www.avsforum.com/threads/dsd-over-hdmi.2533913/page-2) of this being possible.
So I am extremely confused 
EDIT: @Saturn94 – I took a look also at my copy of the Oppo 103 manual, and a different parsing of that piece occurred to me. It could be saying that the HDMI Inputs can accept: (a) either [6ch/192kHz] or (b) [8ch/96 kHz PCM]. It’s a matter of what the scope of the “PCM” qualifier is. If it applies only to the 8ch, then the 6 ch could potentially include DSD64…