The above was explained ad nauseam
No it wan’t explained why a screen shot of a 10khz square wave couldn’t be shown direct from the Purifi 1ET400A speaker terminals, as the speakers see it, as Stereophile shows a few years ago here https://ibb.co/MnK3mcm (top pic) but now Stereophile also don’t show it without the external filter, because it’s not a good look for their advertisers to show that kind of barely recognizable square wave.
Instead the screen shot that is shown, had been extensively cleaned up after it had gone through an A.P. AUX external -52db LP testing filter (bottom pic), fooling readers/viewers into thinking that it comes out this clean from the Purifi 1ET400A speaker terminals. A hoax in my view.