Ok I managed to get a Marantz SR5008 for $200 so I can at least compare and do some testing. To some of you, technically this might seem silly or ridiculous or whatever, it doesn't matter, I'm writing what I hear, so there's that.
Did some testing and comparing, and in short, the Marantz does sound better than the Pioneer, but is worse in almost any other regard. Biggest improvement is in the treble, it's cleaner and smoother, and the bass section is somewhat different too, maybe a little tighter. I did include the external DAC in testing on the Marantz too.
Again, I'm saying what I hear, whether that might be technically ridiculous or not I don't care... The Marantz sounds better than the Pioneer, but it isn't a match to the external DAC. It sits somewhere in between in audio quality that is audible to me. This is all settings flat or default and pure direct on all tests, and then even with some features or options engaged.
But, setting up and adjusting the Marantz... Boy is it terrible... Things as simple as adjusting subwoofer volume, you have to turn off music, go back into the deep settings in the GUI on the TV and adjust the level visually only on the screen... The worst way the adjust any audio. Most settings are like this.
Audyssey on this model. It's bad. It's worse than the Pioneer's MCACC which isn't really known to be a great room correction software, plus you can't tweak anything. I know it's old, the new XT32 is supposed to be better I really hope it's much better than this, but the Pioneer is already two years older than this Marantz. When I ran the room correction the sound got messed up, got the mids so scooped and the rear surround speakers so loud they overwhelmed the fronts by so much it actually made me laugh . It just sounds way better with it off. Another stupid thing about it is, you can't access some settings unless you run Audyssey... Why, just why. The Pioneer doesn't have any of these limitations, while the Marantz is full of it.
It took me about 2h to get everything set up almost the way I like it (almost cause of its many limitations and lack of options), and looking at the inbuilt small display, I have no idea what the current audio mode is selected. It took me about half an hour on the Pioneer and have clear visibility of what mode I'm in. On the remote you can't control any useful functions related to audio unlike the Pioneer without getting into the GUI. You can control literally everything on the Pioneer (except the Graphic EQ) without going into the GUI and while audio is playing so you can hear the adjustments real time. This is just the tip of the iceberg of how limited and non intuitive the Marantz is compared to the Pioneer. Some audio functions are even only available on the front panel buttons... I also don't know why, I couldn't find those to be adjusted on the remote or the GUI. They may be hidden somewhere where I might have missed, but if they are that hard to find, again... Why??
So, except for the sound which is audibly better than the Pioneer, the Marantz is a disappointment in almost every other regard for my liking. This model at least, I really hope newer models are better than this. Seems like this Marantz at least, isn't meant for people who'd like to have more control over their sound and setup, in a convenient way.
I'll use it for a few more days to see if I can fine tune it further, but it already lacks A LOT of options and convenient features that the Pioneer has. And I'm only referring to the sound options and features. So far for me, the Pioneer is much enjoyable to use with an external DAC, than the Marantz on its own.