Currently have slightly over 150 hours on the Empyrean with leather pads, leaving it till about 300 hours before any critical listening. I would say that this headphone has one of the biggest burn-in progressions that I have ever heard.
From 30 - 50 hours, I thought I had a problem with the headphones as well. Sound was closed in, sounded veiled and bass was quite boomy.
Things got a bit better at the 80 hour mark, sound was slightly clearer, less sibilant, but bass was boomy and highs were strident. Female vocals sounded quite harsh and vocals were presented in a very forward manner. I thought I was listening to the velour pads then instead of the leather pads. The sound was that muddy.
At 100 - 120 hours, the veil over the sound seemed lifted, but the mid-bass seemed to have disappeared as well. Vocals still had a tinge of harshness to it around the edges as well as the highs.
At 150 hours, the veil has totally lifted, vocals and highs are quite smooth and a pleasure to listen to, mid-bass is back but never boomy, with just the right amount of slam to it, the soundstage is much more holographic now, vocals and instruments are not presented in a forward manner but take their own place on the soundstage, soundstage has slightly widened with good instrument separation, height slightly increased as well.
I have the Audeze LCD3-F and Hifiman HE-1000 v1 as well, I would say the Empyrean sound signature is somewhere in between these two, it takes the best qualities of both headphones and this makes it a really fun headphone to listen to. These are now the headphones that it is truly deserving of being a flagship headphones.
I also spent some time at my local audio store to compare the ZMF Verite in Silkwood and Empyrean with velour pads. I would say the Verite sound has more body to it, but sounds much darker than the Empyrean. Transients and dynamics are better and quicker on the Verite, but the Empyrean resolves slightly more detail than the Verite. I went for the Empyrean in the end because well, everything about it just sounds right.
Hope this helps