If I may share my input, I’ve owned all 3 simultaneously, and still own HE6 (Andrew reviewed my actual pair yay).
To me it’s the HE6. It has the biggest initial impact, but definitely not as rich or weighty as LCD4. HE6 has the speed going for it, but is less textured. It just has such tight and dynamic bass, hits like a truck. LCD4 has more bass but it’s more smothering and grandiose, like a blanket.
D8K Pro is also on the fast side, and has better detail than either above, but it’s ever-so less weighty in its bass as the others. I do think it’s the most versatile set of these 3 planars though.
To me, LCD4 is better than HE6 off BHA-1 despite HE6 being more tuned to my preference.
On speaker amp, I find HE6 scales to be notably superior to LCD4, which is quite a feat.
D8000 Pro is a notch above both, but be cautious of its etched treble which can be hardcore.