Couple of thoughts FWIW:
-If you are searching for "pure" you want the product that distorts the signal the least. That would be a product with the highest SINAD
-Cognitive bias cannot be escaped no matter how well intentioned an individual. For example, I don't think people are lying or intentionally stating something that isn't true when they claim the NAD T758 V3 (the worst measuring AVR) sounds better than a Denon even when no EQ is active. Take a look at
THIS . It is amazing that our opinions on what we believe have any validity at all.
-Whether something sounds better with EQ on with both systems is another thing entirely. Dirac could (and probably is) in many instances better if doing full range EQ in particular if a person isn't doing some after EQ measuring with Audyssey.
-I would think in order to hear differences with no EQ enabled between the NAD 778 and the Denon x8500, it would need to be a very quite, dedicated room, and you would need to be listening at a quite high volume. For example listening at -20db comparing them, I don't think you should even expect to hear a difference between the two.
-In my opinion (which I know has little value!) it depends on how certain you want to be than noise/distortion will not be an issue in your system (both with amps and dacs). The close to 100 you get with Dacs/Amps it would seem you have little to worry about. The closer to 60-70, it would seem there would be cause for concern that noise/distortion would be a problem.
-It will come down to your listening environment (how quite it is), the volume you listen at, the quality of your speakers (what kind of level of distortion are you getting at your listening volume), and how well can you detect distortion.
Whether one believes statements about the NAD sounding better than Denon (or any other brand for that matter) is certainly up to you. But I just would never consider the validity of a claim where someone claims a worse measuring product sounds much better than a much better measuring one, but that is just me.