I've heard a lot of people describe Marantz as "warm" and Denon as "neutral".
And I've heard a lot of people describe Hillary as trustworthy.
We're trying to tell you don't blindly believe what people say. Anybody can say anything... especially on the web.
An audio system has to satisfy 2 criterion... Accuracy and Preference.
The electronics strive for
accuracy in their ability to amplify & reproduce the source material without distortion. (Note: Your MP3 files are digital... ones and zeros. How could any AVR make ones and zeros sound more warm or more neutral?) Their
preference lies in their available features.
Speakers have the same 2 criterion. However, listener
preference plays a much bigger role than in electronics. Some people like "warm", some like "neutral". There are an infinite number of shades in speaker tones, even among the most accurate. That's why we always say the best way to choose speakers is to listen to them.
I would encourage you to develop a habit on any audio forum or discussion. When someone makes a statement like, "Marantz sounds more warm", ask them to show you what in the specs verifies that. Push for a technical explanation, even if you don't fully understand all the technical jargon. Someone who
really understands a technical subject can explain it clearly to a non-technical person. (Think of an engineer explaining a problem to an executive... or Abby explaining a problem to Gibbs.)
For your 2 final AVR choices, they're made by the same company and their
accuracy will be the same. So look for any differences in features, (
preferences). I suspect you'll be completely satisfied with either.