Received this beauty along with Momentum 4 around the same time.
Long story short, I decided to keep these over M4.
With that said, IME, I actually think M4 sounds better. Much better balanced anyways. At first listen, Px8 is very oddly tuned. Mid bass bump is very noticeable and can make male vocals and certain tracks sound congested and compressed. What I like the least about the Px8 is the noticeable sound difference between ANC on and off. I like it better with ANC off and I'm just glad that option is there.
Comfort is superb (for my head) due to aggressively angled driver housing, as well as the fit/finish. Build quality IMO is light years ahead of Px7 I used to own. This is one of few HPs I can actually wear for hours on end without fatigue. Based on my usual sound preference, I shouldn't like the Px8, but I do. And I like it a lot. IMO, Px8 is not so good for critical listening. From that perspective, I completely understand Resolve's POV and anyone else critical of Px8's SQ. But as a lifestyle piece, I think these are fantastic. It's a rich, creamy, and pleasant listening experience, and one where I can easily immerse myself in the music (once I got passed the initial shock of how wrong it sounded) without being judgmental at every turn. In the end, that's what is important in this category (to me at least).
Bottom line, my head initially told me to return the Px8, but my heart told me the opposite.
Px8 will definitely be my guilty pleasure. If you like the PX8, great, and enjoy! If you don't like the Px8, great, and hope you find something to your liking.
p.s., all listening was conducted using S22 ultra connected to BTD600 for aptX Adaptive over Roon ARC.