Another big consideration is the quality of the volume control on the CD player. If this is not of high quality it will degrade the sound and will largely if not more than offset the benefits of skipping the preamp. I'm not familiar with your Marantz CD player, but I'd be suspect of the quality of any CD player's volume control priced under $3000. I'd echo what albertporter said and mention that this is obviously a very system-dependent issue, but if I were you I'd at least try a couple high-end preamps(Pass Labs, Ayre, ARC, etc.) to see what happens in your system. I might also try an Audio Aero Capitole run directly to the amp in your system to see if that makes a bigger difference than adding a preamp--lots of people seem to like going that route. Best of luck.
Tim
Tim