It makes sense that you prefer the Marantz since it has been good to you. I think there are more Denon/Marantz owners than Yamaha here.
I owned the $7500 Denon AVP-A1HDCI, which is much higher-end than the Marantz SR-7012. I think my Yamaha CX-A5100 sounds every bit as great as my AVP-A1HDCI.
Everyone has a different experience.
I just do not like the mirage that Yamaha is considered "ultra reliable and bulletproof" and every other manufacturer plays second fiddle. I see a lot of bogus comments about Yamaha too, such as "YPAO is better or as good as Audyssey XT32 (major bogus claim!)" and "Yamaha is reliable, the others are not!". It is ironic the first Yamaha I bought, which I jumped on the bandwagon because of so many people claiming they are sonically superior and built better, was defective. I found it futher ironic than the Yamaha RX-A1080 did not sound as good as my expectations, which were based on what I can only conclude was bias.
I found YPAO and Pioneer MCACC very similar, but actually though MCACC advanced did a better job correcting my room than YPAO with RSC did (sounded lifeless with it engaged, tried multiple runs with multi-point measurements). I got the Yamaha sounding good, I just like the Pioneer, Denon, and especially Marantz for sound quality better.
Now on the ultra expensive, high-end level like you are talking? I think you cannot go wrong with any of the offerings from any of the receiver makers. You are going to get top-notch components, build, and the highest-grade power supplies and circuitry. I have never felt the need to have a receiver that expensive, as the point of diminishing returns is present. Even if I was rich, I would likely own some very high end speakers, but I would likely do a Marantz pre-amp with Marantz amp. I am talking the type of receivers that end up in 95% of homes, as not everyone can afford that type of equipment nor would want to.
I personally have always preferred Denon and Marantz, because I have yet to have one fail on me and I love the features and sound quality. I initially hated Audyssey, thought it sucked the life out of some songs and such completely. Now I understand it much better and have tried every other brand, I would say Denon is more features for the same money but Marantz has a higher-level build and component level that is audibly noticeable.
Compared to Yamaha, based on experience.
Pioneer: More powerful sounding even if in the same power range. Front biased sound after auto-setup, I found I always had to turn up the surround speakers a notch or two after running MCACC. Better with dome tweeters due to a slightly colder sound signature.
Sony: Maybe the most powerful for the given wattage; think they sound better than all but the higher leveled Yamahas and compete well with them even (cannot comment on ultra-high end Yamahas but likely not going to compete well). Better with dome tweeters due to neutral sound signature but drive Aluminum tweeters well too.
Onkyo: Best movie sound, but never liked the sound quality for music much. You can get them to sound good but older Accu-Eq was so-so and sounds dull to me. Maybe the higher end would be a bit better? The TX-SR706 was my first HDMI and room corrected (Multi-EQ) receiver, so they will always hold a place with me but sound quality of the low to mid-tier is the lowest (but for movies it shines, for whatever reason). I also had handshake issues with HDMI starting with even my first one. Mid to higher levels are a bit warmer but overall fairly neutral sound signature. Think it can go well with either aluminum or dome, yet better with traditional tweeters.
Denon: Very smooth and laid-back sound signature, yet sounds good for music and movies and is definitely warm (yet cooler than Marantz). Good with either aluminum or dome tweeters, with aluminum having a slight preference. I think musically they are sonically superior to equal or even slightly higher leveled Yamaha receivers. Not as forward but slightly warmer than Yamaha.
Marantz: Owned the SR5010, SR6011, and now the SR7012. Musically, unbeatable in surround, 2 channel, and stereo sound. Warm sound signature with plenty of articulation and dynamics. Good balanced sound, rock-solid reliable, and all built well/heavy. The portal might not be everyone's cup of tea, personally I like it. Modern AVR have a graphical display but I can see some people not liking it. They were engineered to sound good and it is not snake oil, I can hear things I have never heard in songs and movies (might be combination of the sound quality and Multi-EQ XT32 working it's magic, but whatever it is, it is there!). The only con is they are always going to be much more expensive than the Denon equivalent, but still decked out often with mid to high tier Audyssey room correction on-board. The Multi-EQ editor app for Android and iOS is unbelievably awesome, people complain you cannot tweak Audyssey much...now you can!
Colder receivers will sound better on dome tweeters, ribbon tweeters (which tend to sound warmer). Alumimum and horn speakers sound better with warmer sounding receivers. I have come to this conclusion many times after hearing my various receivers.
These are of course all of my opinions, so take them with a grain of salt. But with me trying so many different products over the years, along with now having good speakers to test them on, I would consider my opinion formed over a lot of experience and messing with sound constantly. I also setup a home studio in my house with pro-audio monitors and have a Umik DSP-1 mic and REW, but nothing to do with any of this.
Just a guy who tries to get good gear that is affordable, has the features I really want, and sounds good to my ears. Not biased because it is a "new toy", never been that way. I actually am very critical of my audio gear, hence why I used to buy and often turn around and sell my older gear because I could not get the features or sound I was after with it.
