I somewhat agree with above statements except I think the "musical" criteria is entirely a matter of tastes. For my tastes and the listen I listen too, both HD800 and K812 are enjoyable
Here's my impressions of the K812 compared to the HD800 :
- A bit warmer with a more downward FR ( This K812 has a close to perfect balance IMO)
- Very good soundstage less wide and deep than the HD800 but as holographic. Imaging is not near as good as the HD800 though. Both soundstages share the same diffuse and laid-back nature.
- Bass are less clean and precise than the HD800. That contrbutes to the warmth but the shortcoming is a slight boominess. very slight. I'm nitpicking here bit Hey we're talking about a TOTL 1500€ headphone.
- More sub bass than the HD800 . I really like the K812 with Electronic music.
- Issues in the treble. sometimes it's really annoying/fatiguing, sometimes not so. Depends on recordings. Overally I have difficulties with this treble.
- Serious lack of dynamics (macro and micro dynamics) so the K812 fails to suck me into the music compared to my Stax or my HD800. I always need to crank up the volume without finding What I look for except harsher treble. with the treble it's the biggest flaw of the K812 imo.
- lack of dynamics induce a serious lack of resolution. K812 didn't offer me the same "true to life" feeling and level of engagement than my HD800 or even the Stax SR404.
I used my Octave/Sonett Rig mostly.
Not a bad headphone overally but not in the same league than the HD800 or my Stax SR404 and too expensive for what it offers. This AKG would be a very recommandable headphone at 6/700€. I place it on par with the Beyerdynamic T1 although I much prefer the K812 for my personal tastes. I prefered the Ultrasone Edition 12 to both despite it's technically inferior and the Ultrasone is overpriced too.
I would have been really interested to compare the K712 and this K812. I loved my old K501 when I owned it but I didn't appreciate so much the K701.
My 2 cents, IMO, YMMV