Update: Interestingly, I ended up buying the Sony XA5400ES. I admit I never got a chance to demo the Marantz (no one around me had one in their store and no one was willing to get it unless I purchased-but would not allow return if I didn't like it!).
To give my final impression first, I am very pleased with my decision.
Now some of the details:
I received a great deal for the Sony and I was able to return if not satisfied. I read great things about it, so I thought why not? I brought it home and ran the player for 2 hours straight before starting to listen. Warning...I don't usually believe in the break-in concept with digital sources, but this player has convinced me. I was told a prolonged break-in was necessary, and are they correct! After 2 hours, I will say the detail was definitely increased over my Musical Fidelity A5. However, the brightness and edge was similar to how I felt with my Oppo 83 and Denon 3910 (both of these players I use only in secondary systems for video playback, not music listening). Because the detail and openness was so good, I decided to stick with it.
Over time (has been about 40 hours), the Sony has smoothed out the edginess but at the same opened up in the upper and lower ranges. Now it sounds more "analog" than my A5. With certain CD's I still prefer the softer warmer A5, especially with poorer quality recordings. The 5400 can really reveal the poor quality of certain discs. However, I can definitely say the majority of my CDs are more "real" on the Sony. My wife who was a "boom box is just as good" person when I married her was able to pick 25/25 times on a blinded test with various music (jazz, rock, classical, even pop) the Sony from the A5.
I haven't even talked about SACD playback yet! I can definitely update and expand more of my impressions if wanted, but let me say again that I am very happy with my choice. For less than half the price of the Arcam CD37 and $600 less than the Marantz 15S2, the 5400 is very difficult to say no to.