If one plugged just the two, FR and FL, of the multichannel analog outputs of a player into the regular analog inputs of a receiver, you could play the audio back in various modes as the receiver can apply processing to regular two channel analog ports. But, any audio information from the other channels would be missing in action. The multichannel analog output ports are meant for the EXT. IN multichannel analog input ports on the receiver where no processing can be had and volume is the only adjustment that can be made since the player is handling everything else already.
Using the two channel analog outputs on a player into the two channel analog inputs on the receiver would allow for processing in various modes, but PURE DIRECT or DIRECT modes will result in a signal to only the L and R speakers and the sub would not get a signal. Use all of the multichannel analog outputs into the multichannel analog inputs(EXT. IN) and only channels with information will result in sound coming from the various speakers of a given setup. So, no love for the sub from an X.0 track using those connections.
While they could decode/process and output Dolby TrueHD and DTS HD Master Audio, I do not believe any Oppo decodes Atmos or DTS:X and instead bitstreams them from the HDMI output. If they could decode/process them, they could send them out of the analog outputs, but the best they could do is 5.1.2. unless they made the two channel analog outputs assignable for two more channels. I don’t think any receiver has multichannel analog inputs to accommodate more than seven channels so, f#%k it.