I would post the same question or better search the Audioasylum Hi Rez forum. Those guys seems to be into these nuances. That being said I use a '14 and the sound on CD is very good indeed.
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I just bought one of these to use for SACDs and I am amazed at how good it sounds with regular CDs. I do not know for sure if it upsamples but my guess is that it does not. Nothing in the information on the Marantz web site indicates that it does and manufacturers are usually quick to provide this information for marketing purposes if their player does.