I sold my Q701 because of the strident treble, anemic bass, and thin mids, and the too distant presentation. The K812 has none of these flaws. The treble soars like silk, the mids are nice and full, without being too thick (LCD-2) and the bass is bottomless and hits deep, fast, and with authority, but not planar slam. There is no real big drawback, maybe minor quibble someone might have, or worse case they might get a lemon pair with distortion and ringing.
The biggest issue for me right now is the build quality, or the lack of quality control on mine. I noticed 2 small flaws. There is a splotch of glue on the inner plastic ring, underneath the earpad cushion. I tried cleaning this off using a soft wet towel, but it's hard as a rock. The second issue is that my right side earpad is rotated about an inch counter-clock wise from where the left side is. So I took off the pads and remounted them, same result, Swtiched pads to different side, and the issue still remained, still off alignment. I then noticed that that plastic attachment ring was mounted an inch or two counter-clockwise to the cup, so that is the cause of the problem and there is no solution unless I rip the plastic ring off and cup and somehow reattach it correctly.
I got dissapointed, contacted Brian at RazorDog and he's taking care of me 100%. I'm shipping mine back and he's sending out a replacement pair as soon as he gets some in stock. So I'm very sad, but also happy about how RazorDog is dealing with my issue. Thumbs up for Brian and another good reason to buy from him.
sorry to hear that you are having issues with your 812 as well, M-13. Hope you get your replacement pair soon!