I need first to tell that both the HE-6 and LCD3 have been modded. The LCD3 isn't mine so I am not too sure what kind of mods except it has to do with damping. I also use a Bakoon, which is a current amp that is known to have great synergy with planars but that few people own.
I will say first that PM-1 has easily the best mids, very smooth and transparent. It also has the most bass quantity/impact but its mainly mid-bass and it doesn't reach as low or is as textured and detailed as the Hifiman or Audeze. I don't find the PM1 dark but the treble can't match the HE-6 or LCD3.
Some people have described the PM1 as muddy but I disagree and it is quite detailed but lacks air so can indeed sound stuffy.
I have mainly used the HE-6 for the past two years and I still absolutely love it.
I was rather underwhelmed by the LCD2 (Rev1) to say the least but the LCD3 is definitely the most fun and impressive out of the 3 headphones. The bass extension/quality is phenomenal, fantastic details and dynamics. Great mids and treble. Imaging isn't too bad but headspace remains quite small and very slighlty congested for my taste, more a front row type of sound.
In contrast, the HE-6 sound more polite and slightly more laidback than the Audeze, so less impressive initially, but provide a much bigger headstage and better imaging with each instrument given more space.
The LCD3 is definitely more exciting and alive but can become fatiguing if listening to very energetic and bass heavy music styles such as techno -Alva Noto- or rock - Pulled Apart by Horses, Future of the Left. But gosh it is exhilarating...
I am slightly disappointed with the comfort of the PM-1, pretty good but not great. I actually prefer the HE6. Sadly the LCD3 like all Audezes is causing me pain at the top of my head and is troublesome after long sessions.
I think the PM1 is a very good headphone only letdown by a congested soundstage.
Sadly issues with comfort and price, mean I am unlikely to get an LCD3 despite being one of the most enjoyable and exciting headphones I have heard.