Then you are all set, no point reading what others have to say about difference in sound quality between those AVRs right?
Even highly regarded PhDs such as Dr. Olive and Dr. Toole had stressed the importance of doing comparison listening in DBT. But then again, back to your belief, none of those opinions and/or findings could change you mind anyway, by the "sound" of it.
By the way, the Denon AVR-X4800H, Marantz C40 have the same parts in the audio signal path, came processors, dacs, volume ICs, opamps, power amps etc., just about the only difference is Denon still wouldn't use those silly HDAMs. In other parts of the world, the two have very similar list price, but in North America, people have to pay a lot more, $1000 more in some cases. So, if I were to choose, I would definitely go with the X4800H, but would take the C40 if I were in Europe such as Paris, or Singapore, because I like their look better, not the C50 though because of its limited info display.
Since you can hear a difference and think the Marantz has "better" sound (even though facts don't support that except in some specific scenario..), my suggestion is, go with the C40 even if you have to pay $1,000 more.