I recently purchased a Pioneer Elite SACD player from Pioneer for a great price and have been really impressed with the sound quality improvement compared to my Integra 6-disk player and Samsung blu-ray player. The difference in redbook playback is significant. It's better, not just different. You might consider spending the $250 it cost to my door.
I don't know how much difference you'd hear going from the Marantz to the Denon just to get the 4 ohm rated capacity. My receiver swap had significant improvement in high current capacity and rated power so I have not heard the effect of high current capacity with lower power output. I'd expect that it MIGHT sound a little better, but really can't say.
The SACD might be a better bang for the buck.
I don't know how much difference you'd hear going from the Marantz to the Denon just to get the 4 ohm rated capacity. My receiver swap had significant improvement in high current capacity and rated power so I have not heard the effect of high current capacity with lower power output. I'd expect that it MIGHT sound a little better, but really can't say.
The SACD might be a better bang for the buck.