I've seen lots of discussion regarding the Px8 bass in this thread. I got my Px8 a couple of weeks ago and have been using them quite a lot. I would probably qualify myself as an audiophile, having had a genuine interest for the last 25 years or so. My preference is generally towards a pretty flat frequency response. When it comes to headphones, I have lots of experience with HD 650, HD 600, HD 25-1, Momentum over ear (original wired), AKG K550, ATH-SR5BT. Also experienced various other sets, such as HD 800 (my brother owned these), AirPods Max, AirPods Pro 2, Bathys, H95, Momentum 4. I would of course not characterize all of these as neutral/flat, but I'd say that the HD 650 probably is my overall favorite that I keep coming back to and that's a decently neutral sounding headphone (although definitely lacking in the sub-bass region). Especially if you compare to pretty much any wireless headphone.
Anyway, regarding Px8 bass: I saw someone comment on a frequency response graph for the Px8 and saying that they couldn't believe they would be 6-9 dB above the reference curve. I have no trouble believing that. These headphones are very bass heavy. It's not just a sub bas hump, as it extends into the low mids (~350 Hz) as well. The effect of this is that tracks with lots of bass and lower mid energy sound very thick. I personally listen a lot to rock and metal and the result of this boost is that chugging guitars and bass drums have an overpowering effect on the upper mids and treble. It quite simply sounds like the presentation is skewed and the lower range has an unnaturally high volume.
To me, this effect is quite uncomfortable and fatiguing. I know there are headphones with more bass, so it's of course not the worst offender. [I tried my buddy's XM3 a couple of years ago and sat there in disbelief at the thick, boomy mess...] Still, I would not characterize the Px8 as having a mild bass boost and I think it's important to make that point to prospective buyers.
With all this said, I must say I'm very happy with my Px8. How come? Fortunately, they offer bass and treble controls that work quite well and are stored in the phones and applied to all sources. After having compared them to most of my other headphones as well as the AirPods Max, Bathys, H95 and Momentum 4, I ended up setting the bass to -6 db and the treble to -1 dB. For context, I usually listen in pretty quiet environments with ANC off. At these settings, sound is still warm and the bass level slightly boosted compared to what I'd say is a neutral sound, but I very much like the result. For much of the music I listen to, I'd probably consider them sounding overall better than my HD 650. One area where the HD 650 wins is vocals. They just sound more natural and lifelike. I also easily preferred the Px8 to the H95, as I found the H95, while pretty spacious sounding, had weird/unnatural mids. It was a short listening session, though, so would want a bit more time with those.
Interestingly, my friend also bought the Px8 last week. He compared them to his AirPods Max and AKG K712 and ended up unknowingly setting the bass and treble to the exact same values as I did. He's not really an audiophile, but he does appreciate good sound quality and he thought the bass boost on the Px8 was pretty heavy as well.
The only wireless headphones I tried that could really compete with the Px8 are the Bathys. They clearly have much more space in their presentation, as mentioned here many times. The stock/flat EQ setting on them is much less thick sounding than the Px8 and they overall felt more dynamic in the lower end. I would also consider them to sound more natural with voices. While I think the Bathys have the edge in terms of sound quality, the overall package with the Px8 is great. They sound really good, are not overly big, very comfortable (more so than the Bathys) and look absolutely stunning. Therefore I am quite happy with my choice and will definitely be keeping them for a long time!