There COULD be differences due to EQ/tone controls/room correction, or different bass management/subwoofer settings, etc.
But, lots of people hear a "huge difference" and then "fail" a proper scientific, blind, level-matched
ABX test. ABX tests can be humbling!
Non-scientific, not-engineering, non-specific terms like "engagement', "detailed", "punchy", etc., are also suspicious.
Yeah, those who reported "huge difference" either heard it for potential reasons you cited, or they somehow didn't apply some sort of logical thinking so instead of asking about why, they should either accept what they heard without questioning, or starting questioning if their objectivity, i.e. effects of bias.
So, just out of curiosity, I sample a few customer reviews on the OP's subject AVR11 from the Crutchfield.com customer reviews, and the following probably tell us something obvious, that while they all feel good about what they bought, opinions varies. Again, that's expected.
customer 1:
Honestly, nothing special. I primarily
bought this for music (not home theater). I have
a few cheaper receivers and the music sounds just as good. I
prefer the sound of Marantz...but in the end it is just personal preference.
Customer 2:
Really nice upgrade
from an older Marantz SR6005. Wanted something a little more musical. AVR11 sounds fantastic, very happy with the improvement!!!
Customer 3:
a great receiver .
It sound very natural .
To me, Customer 3's "natural" would be what I prefer, but then again, it's just his/her perception, to others who also "go by their ears" might say it isn't "natural" lol..
One can do the same by sampling Denon, Yamaha, Anthem, NAD and can expect similar variety of assessments based on users subjective reviews.
By the way, one BB customer reported that the AVR11's excellent sound quality, describing it as
clear and bright. That, versus truwarrier22's reported "warm" sound, so much for diversity haha.