By "RCA," are you talking about analog connections between your CD player and the receiver or are you talking about the digital, coax cable between the two?
If the latter then as John has pointed out, both are sending streams of zeros and ones (digital) and you are using the same DAC in your receiver. Unless something is broken, then the resulting data received will be exactly identical.
If you are talking about a two pairs of analog, RCA pre-outs from your player to the receiver then indeed now the job of DAC has moved from the receiver to the player. There is more room for speculation on a difference there and lot's or arguments can ensue. Many will argue that the difference is not audible.
Also, just to reinforce what others have said. Science has shown that the human brain will always pick out "louder" as sounding 'better'. (A trick commonly used in audio shops to create favor towards a product.) To accurately compare something, one thing that has to be done for certain is that both sources have to be playing at exactly the same volume.
