I was just researching on av reciever and came across many blogs referring to warm,bright and neural sound tagged to receiver brand.
The internet (University of Google) is full of hearsay and nonsense.
We usually make fun of those people.
In Direct/Bypass/Through mode (no EQ or DSP),they should sound neutral/accurate/flat.
If any EQ (auto or manual) or DSP is turned on, then you might get one of those adjectives- warm, bright, sweet, chocolaty, blah, blah, blah like some foods or drinks.