The difference in sound will depend on the quality of the DAC in the player and the receiver or processor. Some players scimp on the DAC so even compressed multichannel in a receiver may sound better than analog 5.1 or analog CD stereo. It depends.

The Oppo 971 supposedly has better DACs than the 980 but its best to let your ear be the judge when comparing the digital or analog outputs to your particular receiver.

John