If interested, here's an article that compares the room correction systems available in 2017. The various versions of Audyssey are described, and are pretty much the same today. They really like the step up to XT32.
Besides the XT32, stepping up from the X2600H gets you 7.2 (X3500H) or 11.2 (X3600H/X4500H) preouts if you ever decide to go with full external amps. The X2600H would have to be replaced if you decide to do that later.
If you don't mind getting 2 more speakers and mounting them, with the X4500H you get the ability to go 5.2.4 right away with 9 on-board amps, and 7.2.4 with an external amplifier (and a trigger to turn it on) later, instead of being "limited" to 5.2.2 for immersive audio.
Speakers like the Polk OWM5 might be suitable for 5.x surrounds and relatively easily placed/mounted. Then the ceiling speakers could be used for the x.x.4 for Atmos/DTS:X
4K/60Hz upscaling is there as well as opposed to 4K/30Hz on the X2600H, but your TV may or may not do a better job of it. Some brands (Vizio is singled out at times) are criticized for its on-board upscaling. rtings.com may help you decide if that's an issue for you.
The X4500H offers over the X3500H/X3600H
Zone 2 allows for custom settings, and you get an ability for a Zone 3.
Internal cooling fans, which may be useful, depending on where the AVR gets located. There are those that would spend extra just for the fans(cooling design in general, including the fans).
Bass Sync for LFE (Not the same as dual sub management in XT32. At least that's over the X3500H. It's not mentioned at all in the 2019 FAQ)
By going with a 2018 model instead of 2019, you give up at least eARC, HDCP 2.3 and bluetooth transmission, if any of those matter to you.
UPDATE/CORRECTION: The 2018 models (X3500H and up, Marantz 6013 and up) do have eARC
Originally Posted by Medal
I appreciate the input and I think I confused what I was trying to say. This picture is basically what my space looks like, execpt there will be a second sub in the same spot on the right and I don't currently have the back right/left speakers as show in this pic..otherwise, the way the in-ceiling are shown, along with everything else is what I'm going for. I got confused with minidsp and the proper use of the channels.
I think regardless of if I pick up those back speakers now or wait, I had the right idea, the room correction options along with minidsp made my head explode a bit.