- The K612 is more neutral than the K712, but not as neutral as the Q701 (going off memory).
- Signature probably isn't that different than the HD600.
- When you put the K712 pads on the K612, it becomes warmer than the K712. So the K612 drivers themselves are actually a little warmer sounding.
- The K612 is really hungry for volume.
- Midrange is a bit more forward on the K612 (compared to K712).
- Compared to K712, it's not quite as detailed and resolving, and has a little more grain to it.
- Build quality feels a little cheaper than K712.
- Soundstage is solid and plenty good for this price. The K712s is a bit more expansive sounding and with more layering and cleaner separation. One of the premiums you get for paying extra (along with the better resolution and greater body).
That's pretty much in line with my impressions of the K612 compared to the K712. Although I personally think the K612 is more neutral than the Q701. It does sound rather similar to the HD 600. What I really like about the K612 is how non-fatiguing the sound is. The K712 can be a tad fatiguing because of the treble at times.