I finally broke down and bought one of these. It's not exactly what I wanted but with it selling for at or close to $700 and the X3800 being $1800 before the Dirac license it was just too good a bargain. I might get something nicer later but I only need 5.1ch and not really a ton of power. If I really need more at some point I can add external amplification. I'm upgrading from a trusty old Yamaha RX-V663 of 2008 vintage and I needed updated HDMI to pass 4K, HDR, DV, etc. to my OLED tv and I wanted Dirac. I was tempted to look at the RZ70 for the bigger power, better DACs, and a few options but it's physically too big to fit in my TV stand.
Anyway, I did a first run with Dirac and it definitely needs some re-measuring of certain points but overall I'm impressed with how well it handled the bass even without DLBC added. My sub never sounded better for sure. Surround effects and dialog are undeniably better as well. (I wasn't using anything before other than measured distances/levels, because 18 year-old YPAO is terrible) I also appreciate the quick adjustment for sub level and center level without pausing a movie and going into the menu, plus being able to do it from my phone. (I know, coming from the stone age)
I'm annoyed that when I want to change the music mode I have to cycle through the whole list, as it seems "direct" doesn't include the crossover settings and sub so I have to go to "stereo" if I want to play music with the subwoofer. There's no real reason to prefer "direct" over "pure direct" since it's just stereo without Dirac or sub. I need to figure out if it's possible to have it default to a different setting and then just program a pure direct toggle on my harmony remote. I also wish I could use different crossover settings on a per-input basis, as what I prefer for music with fairly large front speakers is a bit different from when I'm watching a movie. At least it doesn't seem like I can do that. And when I use Dirac the crossover seems to be locked in place, so while I can use a different Dirac slot for music with a different curve, I can't specify a lower crossover point.
Overall, I'm happy enough with it for the money. The TV sure looks great.