Ahh, there you go… 
You found out !
It performs even better when paired with external amplification. Quite clean sounding the denon 8500.
One can actually experience this by just changing the volume on the fly as you listen to the bass tracks , adjusting the slider up and down in volume on the 2x4hd, you will be able to tell the difference
So hope this helps those of you having a mindisp 2x4hd, u will now have better information on which side of the volume you can increase