While of course it's fair game evaluating this CD player through USB (since it offers such connectivity), there are much better purpose built DACs for that, IMO. I'd think as a DAC this would be better off using SPDIF, but that's just me based on the common statement that with more traditionally minded equipment the USB doesn't seem to be the preferred input. I'd like to give the Marantz the benefit of the doubt, thinking it'd show better CD-quality performance in its more native environment...
Naturally, I can't prove it and I find the provided data -once again- thought provoking.
I should also note my "audio shrine" doesn't use USB. I do stream to it from my computer (and Spotify) using a 2010 edition Squeezebox Touch and then its coax SDPIF. My work computer, which I use countless hours, does use USB to (as of today) JDS Element 3. I should note in either case it's a matter of the UI on each platform. I still find the SB Touch provides me with a better music UI than if I did it over USB. I like JRiver Mediacenter for many things but certainly not for the UI - I can deal with it with a mouse on my workstation while chained to work, but not when I am sitting on the couch after work chilling away...
I also do like Amir does provide an opinion on the UI - indeed to me the old CD way (never mind vinyl) is a user experience I'd rather miss. Fidgeting with physical media, trying to read super small fonts, dealing with 8 different remotes with small button and that often are impossible to use in the dark - I have seen the light...
I used an Accuphase DP-65v for many years as a DAC - its SNR was up to 118dB (it supported up to 24bits through optical/coax SPDIF) , the DNR was 98dB, just a tad above the 96dB you'd get out of a CD (in theory). To that that may mean that CD players are designed to sound great for CD playing, which honestly is fine enough for me. I know we are SNR and we're supposed to prefer much higher numbers... but I don't think the DP-65v represented any sort of bottleneck to my musical enjoyment, I just got rid of it because it was unwieldly and huge and simply didn't fit into my smaller new environment, especially when matched with its E-306v integrated amp sibling.