I dont think alot of people is disappointed with the player itself.
The issues most of us is having, is mainly with the Engine Prime and the long wait for firmware updates/ bugfixes.
(hopefully Denon will be able to keep their words and deliver the upcoming updates in about 2 weeks from now)
The player itself, is really Nice!
Yes there are some benefits in having the X1800 mixer and not some other mixer.
Amongst other things you can take full advantage of the color on the Cue buttons (headphones selector) on the mixer so it matches the chosen deck/ layer.
The fader start/ crossfader start function as well.
The build in hub works perfectly.
There is probably other things as well, but I have only used my 2 SC5000s with the X1800 mixer, so these are the things I have seen/ experience. (and come to my mind at this moment)
Maybe someone who have used / uses another mixer, can point out even more things.
Best Regards Engell