So you don't think that head-fi is at all influential in helping consumers make purchasing decisions?
No, I do, just not to the extent you say, and definitely not directly. The Youtube vloggers and tech sites that helped the ATH-M50 sell so well might have stumbled onto head-fi or Tyll's site in the early days while they were doing research, but their readers/viewers who ended up buying the cans most probably don't even know we exist.
It mostly depends on price points. Anything under $200 would probably get more marketing via general tech mags/sites and even general consumption news outlets, along with the social channels these establishments spread their news with. The midrange $200-$500 category would probably fall under the lifestyle category, gaining interest via said lifestyle publications, Apple-centric publications/blogs (because Apple is more lifestyle centric these days), and probably tech sites and Youtubers as well. Exceptions being the pro oriented offerings in that price segment which tend to get a bit more traction here, but generally get last word via the more pro oriented forums and publications. Head-fi opinion probably has bigger influence over +$500 segment, which is generally a price range where interested parties would be inclined to do more personal research, though we have to bear in mind that people who spend that much on headphones are of a small minority.
Someone wanting to buy a Focal flagship would definitely visit Head-fi, even if he/she first heard about it while reading The Verge. For headphones like those from the B&W P series or B&O offerings, I wager most of the coverage these companies get come via lifestyle related sites/blogs/vlogs and social feed aggregations, with the reviews of the Bluetooth models in particular capitalizing on Apple's timing to ditch the 3.5mm jack, even if wireless headphone sales in the first-world already starting catching up to wired headphone sales a couple of years prior to that.
The only general influence/opinion overlap I've seen over the last couple of years has been between Head-fi and certain Reddit groups. Reddit as a whole is pretty much a crapshow though, so I don't think we should be too proud about that.