My first try with the NAD was without running Dirac and it literally brought the speakers to life, specially in clarity, something that the 4700 (that had been confifured with Audissey) was absolutely not doing. After running Dirac the difference gap is even bigger.
Anyway, it's not a competition, like I said it's my experience and I tested both almost side-by-side.
I use Krix speakers (which are 6ohms, and yes the Denon was configured to 6ohms as well) that I was almost putting in the bin after spending a considerable amount in the speaker upgrade. After switchihg to the NAD I have decided the speakers will stay for many years.
Tough to figure why the NAD over the Denon... possibly...
-Were they level matched so they were the same volume? When not level matched, people pick the louder one as sounding better
-Blind test? Cognitive bias is a real thing
-How loud? If not overly loud I think it would be very difficult to tell the difference in a blind test. As volume increases it can be easier with the NAD, in particular if you have sensitive speakers. In quite passages, depending on your speakers and listening distance it is possible to hear hiss/noise from the amps (at least that was my case).
-Setting Denon to 4/6ohm severely limits the output.
If you really want to know for sure there is a difference, you really have to take some care to be sure that other factors aren't causing you to pick the NAD... volume matching, blind testing, etc. There are a lot of factors that can lead to unreliable conclusions if you aren't careful.
It wouldn’t surprise me if in some conditions you couldn’t tell them apart with no EQ enabled. It would very much surprise me if under proper conditions someone would find the NAD to sound better. The Denon x3700 models and higher measure much much better.
I believe the early subjective reviews on this product have perpetuated ”how good it sounds” even without EQ. Most of these subjective reviews online are nothing more than paid press release/talking points, so one should take them for what they are worth... often times a good overview of features but nothing more IMO.