Well.. Really odd!
The Denon X2600H is near Identical with Marantz SR5014- see screenshots and figure out the differences ;-)
Apart from the much better DAC's in the Marantz. Also the Marantz has better power supply and anti jitter circuits.
- Which apparently is one reason for the Marantz's higher price point.
Surely the Marantz ought to sound quite a bit more defined which is also my experience, with the Denon being more bass heavy but also more muddled in the midrange and aggressive in the high treble..
However the latest SR5015 is far too pricey in my opinion at €900-1000 ($1125-1250),
as you can pick up a X2600H at ~ €500 ($625) or even better the X3700H 9.2 channel at ~€1000 ($1250)