I have had these for a few months, wanting to try the electrostatic / large diaphragm experience for cheap.
I use them with Vesper Audio pads which, although not fixing the poor frequency response, do make them much more comfortable and ensure better seal for bass. I put a strip of foam in them to angle them a little and have gently bent the metal headband connectors in a bit as they are were loose on my small head.
Here's my EQ:
Filter 1: ON LSC Fc 40 Hz Gain 6.0 dB Q 0.800
Filter 2: ON PK Fc 1000 Hz Gain -4.0 dB Q 1.000
Filter 3: OFF PK Fc 2000 Hz Gain 2.0 dB Q 0.500
Filter 4: ON PK Fc 3300 Hz Gain 2.0 dB Q 2.000
Filter 5: ON PK Fc 5600 Hz Gain -3.0 dB Q 4.000
If you have the velour pads just turn Filter 3 on as that approximates the difference. The low shelf is obviously to taste, sometimes I prefer 9dB at 0.6 Q for a warmer sound. Filter 5 is very subtle and not necessary unless that region bothers you, which I've found it often does me.
I do think they sound very good with EQ. They sound different to my HD6XX even though the EQ'd response is very similar - in particular they sound brighter in a way that belies the measurements and I suspect is due to the soundwave created by the large diaphragm interacting with my ear to create a different perception of treble than what is seen on a dummy head. I've noticed some spatial qualities, though not really "soundstage" which is a concept I struggle with. More like separation and openness though I realise these are unhelpful and overused terms. I get a bit more of a feeling of bass around my ears as well in contrast to the HD6XX and IEMs where the bass feels narrowly transmitted into your ear canal.
I suspect the electrostatic technology has nothing to do with it and that any perceived benefits are due to having large, open cups and diaphragms. This makes me think that planar magnetic headphones with similarly, or even larger, drivers would have the same benefits - and without the need for an energiser and the occasional appearance of an annoying whine. So now I'm tempted by those nice big (and much more expensive) Audezes.
I have flat-plate coupler measurements which I can share though they're of limited use; the cups are so large I have to take a lot of measurements and average as the response changes depending on position, so it's hard to know exactly how it relates to on-head response.
I'd like to be able to correct the response acoustically as there are electrostatic heapdhones with better response. I have no idea what kind of damping needs to be done and am not keen to open them up really.