Just come across this thread. I would recommend the Abyss TC. Yes it is a strange fit, and it does need a fairly powerful HP amp. BUT what you get is Stax 009 details and speed, mids of the Utopia, and bass of the LCD4. It sounds impossible, but it IS right there in the Abyss TC.
I still have my LCD4, but sold my Stax years years ago. The ethereal floating soundstage and forward treble pushed me away TBH. I did enjoy if for some time, but in the end, had to admit defeat with it, and also realise it was not accurate.
The Utopia is nice, easy to drive and good fit. BUT it does nothing top level IMO. At 4K it should TBH. The RAAL is top level as regards imaging and treble detail, but fails in the lower bass and weight to the midrange.
The hifiman Susvara is also very good, 'good' at everything, not superb at anything. This is to my ears. And the price and build quality are not good aspects.
That is my view. The Abyss TC gets real close to high end (big) speakers, does enough things superbly, and what is left, I am not concerned about. If we consider what we are asking any high end headphone to accomplish, i.e. play the full frequency spectrum from a single driver in a tiny chamber very close to the ear, it is quite amazing headphones have actually got to this seriously high level.
I just love the personal soundstage, the inmate performance and micro details you can get with SOTA headphones. And others must think the same, as it is an expanding market. Look how many HPs retails above 5K, not to mention dedicated amplifiers to match.