I also have an emotiva xpa 5, currently use it as an xpa 3, so channel 2 and 4 is unused (run my sides from the avr direct)
I bought the emo since with my previous pioneer elite lost all dynamism and started sounding loud and shrill in movies at just past -20 mv. The emo was a noticeable immidiate improvement , but with this denon the difference of using the emo or the internals where negligible at best even at say mv -14, I might perceive the center and speach just a touch more legible, but that might just be in my own perception.
I keep it since I wouldn't get much from it (1gen xpa5) and selling would be a hassle (its to heavy to ship normally) and it wouldn't get me much. And having the extra peace of mind in regards to surplus power and wattage is well worth it, and with Atmos coming up having a few extra amplification channels around could be nothing but handy :-D
In my testing I also discovered that for the sound to mesh while switching between the internals and the xpa required a full and complete recalibration, just checking levels did not do it all.