Hello higenbs1,
If you go to
http://www.marantz.com/hifi/europe/ you can compare the standard 5400 and the OSE version side-by-side.
Mainly, the differences come down to better construction and some audiophile quality components. These may well make a real difference to the sound quality - I have heard neither of them.
I would have doubted that the 5400 is better than the Denon DVD-2900 for CD playback. After all, the DVD-2900 is more expensive than the 5400 and has less to do. So, the 5400 is bound to be making compromises somewhere.........
TH