HD600 VS DT880
The HD600 and DT880 sound very different. The Sennheiser headphone having a more relaxed and warmer sound while the Beyerdynamic phone to have a more lively, involving sound. The treble is very different between them. Just liek with the DT770, the HD600's treble kind of sounds very muted or toned down and lacks detail and extension while the DT880 has lots of detail and extends way up there. The DT880's treble is also far cleaner sounding and hazy sounding like the HD600's, but the HD600's treble is still nice in my opinion. The treble on the HD600 can tame normally brightly mastered music as well.
The midrange on both is as stated before with the DT770, but the DT880 has far more detail to it's midrange than the DT770 has but also is a lot more resolving and detailed than the HD600's. The HD600's midrange can sound a bit hazy and congested on some pieces, and can also add some unneeded warmth to already warm recordings. It can also add more warmth to recordings that lack some midrange body. It's also good for covering up recording errors.
Bass on both is still very different. The HD600 still has a one tone sound to it compared to the complex bass of the DT880. The DT880's bass has a lot of texture to it and can easily trump the HD600's bass. The DT880's also extends even deeper than the DT770. The HD600 has decent extension to it but lacks some texturing. One thing to note is that the HD600 does have more body and impact to it's bass than the DT880 does, but the DT880's bass sounds more realistic and natural.
The soundstage on both is very comparable in terms of width and depth, but the DT880 sounds bigger. Layering on both is good and the DT880 has the edge on separation and air this time. The DT880's has one of the best stages in the mid-fi category I believe, and is more accurate as far as where sounds would be originating from.