I've had mine for a few weeks now so it's a good time to give some impressions. They improved with 100 hours running in, but continued to improve slightly but noticeably over the next 100 hours or so.
My 'frame of reference' is the AKG K812. My headphone system uses the excellent Gryphon Scorpio CD player, a really lovely player.
I have two fairly similar valve headphone amps, one using 7N7 and paralleled 12SN7 valves, the other using paralleled 7N7s, both with good output transformers; both are excellent.
The K812s sound good on this setup; I've heard them sound awful with a lesser Cd player and solid state amp.
The PMx2 is totally *amazing*. The music is simply so enjoyable it puts a smile on my face, tingles down my spine, just beautiful.
It's really worked out for me as these are the things I find missing from the K812's, excellent though those are in many ways.
So may I give sincere thanks to Alex for his fine product and also the care he took to ensure they would be suitable, and to the posters here ... comments were spot on. In particular I mention Ray for his shootout details (truly excellent!), and for personal dealings.
Now some specifics.
All the following things are superb.
Transparency; tonality; purity; naturalness; engagement with the music (tapping my feet, hard to do in bed!!!); the 'shape' of music (Mozart having that Mozart lilt and shape, making me want to conduct); separation of instruments; proper individual character of different instruments (related to tonality); fast, clean leading edges making plucked strings and percussion sound good; resolution/timing which separates out fast sequences of notes. I'm bound to have forgotten many things.
And above all, these things are delivered with *class* and BEAUTY.
One funny comment which I hope is appreciated in the right way. I find that mid range hifi sounds like, well, reasonable hifi; high end hifi sounds better in the ways hifi is mostly described ... bass, treble, dynamics etc; but the highest level of hifi just doesn't sound like hifi !!!
To me, the PMx2 just doesn't sound like hifi, it's better than that. See how I describe things above and you may see what I mean; no mention of bass, treble etc (OK, they are *fine*), but I'm appreciating things at a higher level.
To set some kind of benchmark I'll mention my main system. I'm fussy about sound and make my own valve electronics to get the sound quality and nature I like.
Main source is Teres turntable, Moerch DP8 arm, Zyx 4D cartridge (a lovely combination). Valve phono stage (better than Aesthetix Rhea in a head to head), '27' valve line preamp; '45' parallel single ended valve amp; good speakers of suitable sensitivity. The 45 amp is far better than typical 300B SET amps.
Second source is Heed DT/DA cd system, decent but below the vinyl front end.
This system is mainly used for classical, folk, jazz, popular. I specially love female vocals.
The PMx2 with good source and amp sounds in many ways like my main system and gives me similar pleasure; it's the only headphone setup that has ever done that. No, they don't sound the same, but the nature and strengths are similar. For one thing, female vocals are utterly gorgeous on both my main system and the headphone system with PMx2.
Some music I love. I was about to write 'which shows the virtues of the PMx2' but *all* music does this!
Melissa Menago; highly transparent
Amber Rubarth, Scribbled Folk Symphonies; highly transparent; sweet, and also note the 'growl' of the cello
Tierney Sutton, After Blue; lovely vocals, lots going on, superb piano
Calamus, The splendour of Al-Andalus; thanks Ray! Lots going on, all well resolved, fine leading edges, fine tonality, musical
Eduardo Paniagua, Cantigas of Toledo; Eduardo is the main man in Calamus! Similar comments apply
Halie Loren, Stages; live, and in the best way it sounds it, fabulous
Mozart, Flute and Harp Concerto; Piano concerto no 21; City of London Sinfonia. I rarely listen to classical on CD but this sounds good, and it sounds like Mozart (not all systems do this IMHO).
Anything else by Halie Loren or Tierney Sutton; anything by Dave Carter and Tracy Grammer.
All the above sound *fantastic* on a good system.
Sorry if I ramble on and bore you ......
Best regards
Mike C in the UK