HIFIMAN - SHANGRI-LA

There's the biggest (artificial) and then there's the most natural sounding stage. When it comes to artificial sounding stages, I would say the Sennheiser HD800S/Hifiman Shangri La Sr have the widest stage whilst the Stax SR-Omega has the most natural sounding stage.

It’s been a while since I had a pair of Stax, but I remember that soundstage as amazing, so I’d say those or the Shangri-La, which are pretty astounding.

There are no perfect headphones. Honestly, there aren't really any exceptionally good headphones, either. Technical capabilities are all that matter and EQing to your personal target matters more than any amount of stock tuning. Whether or not a headphone can handle being EQ'd to your preference is pretty much the last thing in the way, for example you can't get any good bass out of a 6XX or HD800s, it's simply not possible. I could be content for life with my modded and EQ'd HE6se v2 and Shangri-La, but that's still 2 headphones, and while my modded and EQ'd Shangs might slam harder than a stock Focal Utopia, they still can't slam like the HE6(which slam hard enough to snap a Focal headband on their own lol).

Nothing will ever be more important than isolation when it comes to gaming. That's the sole reason IEMs can be so good. I'm going to say this early, the HD800s are straight up not good for competitive gaming. I wouldn't put them in the top 20. All they have going for them is imaging and a complete and total lack of ability to deliver any bass information that could obscure sounds. They have all width and no depth or height to the soundstage and on top of that, the width they do have is extremely exaggerated. There's no middle distance in the soundstage, a sound will move from sounding 30 feet away to 10 feet away in almost an instant and that's the opposite of accurate. It's outright deceptive to you and it's an instant disqualifier for comp gaming for exactly that reason. IEMs can pull ahead of the HD800s from isolation and tuning alone. They don't need a massive soundstage, having an EVEN soundstage with accurate placement and separation is far more important. It's not uncommon for good IEMs to have more stage depth than the HD800s, but there's none that have the stage width and that's enough right there to showcase how out of place that artificial stage width is. I've chased stage size and hit the end. The Hifiman Shangri-La make the HD800s stage seem like the size of a diving helmet in comparison. Nothing stages bigger. They're capable of easily 2 or 3 times the stage size of the HD800s and I would never reach for them over some of my other headphones or IEMs if I wanted to sweat on some comp shooters. There's ~$100-150 IEMs I'd take over the HD800s for gaming and probably 15-20 headphones under $1500 that are, either with or without EQ, leaps and bounds better than the HD800s in terms of capabilities for comp shooters. Most IEMs are pretty tricky for gaming, most aren't really all that bad but it's fairly rare that any are actually exceptionally good and with fitment being so personal, it can eliminate 80% of the options instantly if your ears are a certain shape or size so it can be a nightmare finding a good set for some people but great sets are out there at every price range and getting over the fear of EQ and learning to use it gives you easily 5x the options instantly.