You are precisely right, I am a fan, a really big fan...... but that's only after listening to the competitors.
I have absolutely no problem with that; the reason being, as we know.... everyone is entitled to their own opinion.
See, the thing is, it isn't hard to build a neutral class A/B amplifier. Most receivers made by Denon, Onkyo, Marantz, Pioneer, Harman Kardon, Yamaha and plenty more, use Class A/B amplification. So long as a receiver has a hefty power supply and solid output stage they are going to sound pretty much the same. When you get a different receiver it is feasible that it would sound slightly different, and ever so slightly that only those with super acute hearing would notice the subtle differences between them.
If you bought a receiver and it suddenly sounded phenominally better/different than the one you had before at higher volumes, then it would be safe to assume that the new one has better drive cabability or more power, or both. If it sounded better/different at any volume, then assume the one you had before was faulty or the new one is faulty, because they shouldn't sound hugely different, or sound different at all. Other than power and drive ability they should sound pretty much the same, and like I said, if they don't then one of them has a fault.
Also, where the receivers set up the same way with the same room parameters and speakers? If an autosetup was used it could be different depending on the manufacturer, doing a manual setup with an SPL meter and other measuring tools would need to be done to ensure that each receiver was set up optimally for the parameters.
A receiver should not affect the sound as some would think it does, if set up correctly and used within its design parameters (power limitations) they should sound almost if not completely one in the same. The things that dictate you sound "quality" are source material, speakers, and room accoustics, or at least an overwhelming large part.
The way you put it, it sounds like your Denon vastly supercedes any other receiver you have heard, but under what conditions was this done? Did you level match, did you do a DBT, where all speakers and arrangements the same? If it sounded so hugely different then you would have to assume that receivers heavily color your sound, but they don't, they are as close to neutral as possible.
I have done some, not much but enough, level matched DBTs in the past when I had a speaker selector/amplifier selector, and I have to say I couldn't tell you the difference between one receiver or the other, given that neither was pressed to extreme levels of output.