K612 pro has fantastic mids as long as you feed it good quality recordings and power it well with a good amp and DAC. K612 is somewhat hard to drive due to its 120 Ohm impedance combined with pretty low sensitivity. The mids that it produces are very refined, articulate, a bit forward and exciting with a very natural timbre and very high detail resolution. Vocals certainly sound great through the AKGs - very present and realistic.
Compared to MSR7, I think K612 is the more natural and effortless sounding headphone. With K612 you will get a much greater sense of space and instrument separation than what the MSR7 is capable of. This is not surprising considering that the AKG is an open back and the Audio Technica is closed back. K612 also sounds more dynamic and more tonally balanced than MSR7. I find MSR7 to be well balanced, but just a bit lacking in bass weight and lower midrange presence. and a little too forward in the mid to upper midrange. K612 is more neutral to my ears, especially in the bass and lower mids, which have more appropriate weight and presence on the AKGs. The rest of the midrange is also just a bit more even on the K612 I think, although it does have a bit of a boost in the mid to upper midrange, sort of like the MSR7, but less pronounced, which I think is a good thing - it makes the mids more exciting to listen to.
The treble is a bit clearer and more resolving on the MSR7 I believe, but just a bit. Both have excellent treble quality and close to neutral quantity. K612 has treble resolution of a solid mid level $300-$500 open back headphone. MSR7 has treble quality that rivals headphones closer to the $1k range and maybe even higher. However, MSR7 is a closed back headphone and doesn't have the spatial qualities of good open back headphones, so while its treble is extremely good, it still can't make it as open sounding as the good open backs. K612 doesn't quite match MSR7's treble quality, but it still has a more spacious and open sound.
Overall, I would consider the K612 a nice upgrade over MSR7 for relaxed listening at home/in a quiet, calm environment. MSR7 is more forward and exciting to listen to, but it just can't match the effortless dynamics, spaciousness and seamless tonal balance of the K612. To put it another way, MSR7 sounds like it's a very capable headphone, but one that is also trying to show off everything that it's got in a rather aggressive, "in your face" manner. I would say the MSR7 is a bit rude and arrogant... childish perhaps?
K612, on the other hand, is far "calmer" than MSR7. It sounds more nature, relaxed, subtle... But also has more "swing" and expression. So if MSR7 is a very talented, but mentally unstable 16 year old teen, the K612 is more like a generally mature and well behaved, although slightly less talented 20 year old young adult. I say generally mature, because the K612 still has some emphasis in the mids that make it just a bit more forward and exciting than a perfectly neutral headphone (something like HD800 or HE-500 - those crazy talented, but very mature and reserved 30-somethings
).
