You have the same TV as I do Zooie! I run a 7.1 setup with a new Denon X1400 receiver. I've done extensive testing and also found iTunes movies have always been of better quality, especially when it comes to AQ, particularly the LFE just has more oomph.
Now with MA, and since my digital library is so large, I can't make heads or tails of where to watch my movies, in the 'purchased section' on my ATV 4K or the VUDU app. I don't buy the films directly, I get the codes from the BDs that I purchase. If it's a fox title, I always choose iTunes over UV since I've noticed better quality in iTunes. Now with the 4k and licensing issues, I don't know which versions to pick when I have to make a decision with my BD redemption code. Plus, I often see movies in my iTunes library listed as 4k, though when playing they are not. I presume this is a licensing issue as well.