FLAC files --> Schiit Bifrost (uber upgrade) via coaxial cable --> Schiit Asgard (not the Asgard 2, just to clarify) via the Schiit Pyst cables--> Sennheiser HD 600 (stock cable, zero mods, zero break-in time).
I received mine today and have been listening to them ever since. I was previously using a Grado SR60 that I originally bought in 2005 since my Grado SR225 seemed have developed an issue with the left ear cable, likely due to spinning of the ear piece. I was a bit shocked to hear how good they sound straight out of the box. I was also surprised to see that there wasn't much of difference in where I keep the volume knob on the Asgard set. From what I read, the higher impedence of the HD 600 should have likely required more of a difference in the volume knob than I saw. With the Grados, (if you think of the volume notch as the hour hand on a clock) I had the volume at 8:30 for normal listening. I never put it above 10:00 or 10:30 for any extended period of time. With the HD 600, I have it loud at about 9:15. I will likely have it slightly lower for future uses. Onto the sound quality...
I took off the Equalizer setting I was using to correct for the sound curve in the Grados (a bit more bass, a dip in around 8khz to compensate for the Grado spike). I was surprised to see how close it was to the Grados + EQ, but better. The bass is tight, clear, plentiful, and not bloated at all. It sounds a bit deeper than the Grados, but also quite correct to my ears, as far as headphones go. There doesn't appear to be mid bass bump, which is nice. I like accuracy. The mids are nicely balanced, not scooped like what I was expecting from previous Sennheiser experience (circa 2005, a discontinued $60-$70 model fed power via Onkyo stereo receiver). The treble range is clear, extended, and slightly hot in the high hat range at the moment. That could be due to a number of factors related to not being broken in at all, the 8khz scoop that I had on the Grados screwing up my hearing perception, or just realizing that my metal music is produced a bit hot in that range. The big difference between these and the Grados is soundstage. The Sennheisers seem to have a much larger area of sound due to the larger enclosures providing more room for the sound to act within. This results in a more 3d soundscape, provided your DAC/soundcard/source is up for. It also provides the bass with what sounds like a virtual room (pending original song production) to rumble. Because of the soundstage and virtual room bass, it seems to reproduce music with a lot more realism, or more accurately, a clearer picture of the intentions of the producer.
I can't say that I have tried many $400 headphones, or even many headphones in general, but these feel like they are perfectly priced at $400. The fit is snug (I have a smaller head size) but comfortable. It definitely isn't flying off my head when I move like the Grados. Overall, these are quality headphones and I will likely write Sennheiser to thank them for coming through on the discount prices despite the logistics delay. Personally, I would have waited anyway, but I am 30 years old and a bit more patient with life.
Final Fantasy 13-2 soundtrack (outstanding overall production, , probably the best I have heard on any piece of studio music, features lots of layers to sift through)
Cannibal Corpse (old albums sound even worse, new albums sound crushing and feature good production. Note that bass guitar tone coming through clearly)
Deftones - Diamond Eyes (this album sounds damn good on these)
BT (electronic genre, atmosphere on certain albums, decent bass test, good production overall, musical)
Bleeding Through - Declaration (excellent bass guitar production)
Nine Inch Nails - all albums (good production, electronic/industrial/rock/etc.)
Radiohead - Kid A and OK Computer (great production)
Pig Destroyer - all albums (early albums sound atrocious, new albums feature good production but lack a bass guitar, but that comes through in the mix and the headphones don't sugar coat it)
The Contortionist - all albums (Exoplanet features the most accurately recorded Mesa Dual Rectifier I have ever heard. I am even pretty sure the band used either 8 or 7 strings featuring the EMG 808 or 707 pickup (same sound). I know this because i have a Triple Rectifier (sounds basically the same) and a guitar with EMG 808s. the Language albums has good production during the delay pedal moments and sounds very atmospheric at times. That is a treat through these headphones.)
Zedd - Clarity (At louder volumes, the bass on Shave It Up just slams, and you can hear a touch of reverb on it to make it sound a bit like the track has a vague room. I like it.)
Streets Of Rage 2 soundtrack - why? because. (This sounds awesome on these headphones. I love video games)
Killswitch Engage - As Daylight Dies (all sorts of studio tweaking to the sound, but damn does it sound good. I just started listening to the whole thing. )
Ok, so at this point in the review, I honestly am getting way too lost in the music and I still have to get things done before I go to sleep. These are great headphones. If you have them, you know damn well you got something special. For those who don't, check them out. The 650s are really close in design, so keep note for future drops on here. I guarantee that these will work will for any genre. Bassheads might prefer something with a little more ultimate bass extension, but this isn't what i would call a bass-lite headphone. The bass is definitely good. The mid range is where this one shines. It just sounds right.