~1kHz ringing hump is quite nasty with piano indeed, for me.
It is evident when I use HE500s with stock pleather earpads that the pads introduce a ringing node around 750 Hz, which makes piano (especially tracks that have added reverb) blisteringly painful to listen to. It's one of the main goals of my earpad mod, to retain the pleathers' tonal balance while getting rid of that 750 Hz node.
Funny that you should mention the HE500’s in this connection, I disliked them strongly from the first second for the dominating lower mids (when listening to classical music at very moderate levels, as I do*). I could not imagine there would be a mod addressing this, perhaps I should have kept them...(but I also found the bass not very natural sounding for acoustical instruments: a certain lack of aperiodicity perhaps, or distortion, which I also read about later in Purrins comments to his measurements. (I have always been baffled when I see people consider these phones neutral**).
From the different description here & there I got the impression that the Abyss’s are much more neutral overall, hope they will arrive to the shores of Scandinavia soon in the shape of some demo units. Do they sound well-balanced also by lower levels, I wonder?
*I think myself that I listen loud sometimes, but have come to realise that most headphone buffs would find that description laughable, to put it mildly.
**When one click on peoples names on certain (competing) forums one can se geographical data, lists of inventory etc, but how much more telling would it not be to know their average decibel, so to speak!) .