It was my understanding it's not possible at this time (possibly ever) to measure an amplifier's performance on anything other than test tones, pulses, impulses, etc. I'm not sure why you disagree with less being involved in cable design as apposed to amplifier design.
Wait, which part?
Sorry, I agree with the cable part as well, my bad.
I'm not implying that they would mess with the linearity of the amplifier. I guess I may not understand bias, so maybe I should not use that word. Based on measurements done with test tones it's not going to tell us how that amplifier reacts when loaded with a real speaker with music or soundtracks. Perhaps they have people that make final touches to the design using a particular type of speaker to ensure that it doesn't distort audibly. Since we won't assume that Denon and Marantz will perform such calibrations under the exact same conditions it's possible the fine tuning will end with a different result.
That's sort of my point, that is, if you try to "bias", (or the varieties of that word), you are going down a slippery path and never know if where you will end up, could be the ditch. If you aim for accuracy then you have all kinds of instrumentation and knowledge to help you verify whether you meet the goal or not.
Don't get fixated on the amp reacting with music thing. Actually I don't even listen to amplified music much, but for those who mainly listen to pops and even jazz, they invariably will be listening to all sorts of electronic sound processing in the path from source material to loudspeakers. How about electronic keyboards, organs etc., don't they all get molested by electronic gear including amplifiers? If people have no way to know how an amplifier interact with music, you wouldn't even have electronic musical instrument. Don't forget the multiple mics used in studio and live recordings too. So before you need to worry about your own amplifier, you have to worry about those used in the creation of the music and the recording of music.
You an easily imagine why it is a lost course to try and create a brand name sound signature as there will be so many variables to deal with making it practically non sensible, the worst variable is probably human, we all have different hearing perception and preference, there is nothing black and white, wrong and right. Some are also more easily and severely affected by their mood, and Placebo effect.
The right thing for the amp to do is to simply output exactly what is input to it, just make the signal larger and nothing else. Amplifiers (solid state) are designed to have very high input impedance and very low output impedance so they can handle speakers with different characteristics. If not, then you got another problem, that is, even if it is true that Marantz is biased differently as Denon, then due to their different interaction properties with different music and speakers, the Denon can sound like Marantz with speaker A and Marantz can sound like Denon with speaker B. Well I think we both know that is not the case. What those people are spreading are simply not true and if you try to make sense of it, you will be met with massive confusion and contradictions, hence back to the accuracy/neutrality=high fidelity being the best design goals. Leave it to the consumer to "bias" the sound and create the sound signature they preferred by engaging DSP, graphic EQs etc.
I know, not you, but the "rep" and other marketing people. I just hope you are not, and won't ever be the victim.