Here are some general impressions of HD555 after about 40 hours of burn in. Equipment used is MG Head OTL amp, with an onkyo cd player and MSB Link II DAC, with magwires cables.
midrange: This is the strength of the cans imo. The midrange sounds pretty neutral to me, with a slight bit of grain. In comparison to the HD580, the upper midrange is lifted and sounds a lot more forward. The lower midrange is not as warm but still has a lush character. This headphone does very well with vocals.
Bass: The bass sounds pretty neutral to me. I don't detect a bass hump like the HD580. The bass sounds tight, punchy, fast, without any boom or overwhelming the rest of the music. I'm pretty satisfied with the bass.
Highs: similar to the HD580, maybe a little more prominent. But still have that recessed, rolled off character.
Soundstage: This is the weak point of the cans. The soundstage sounds noticably narrower and instruments can tend to sound jumbled. Soundstage depth doesn't sound like its reproduced properly. I'll need to do more listening here.
Overall I'm satisfied with their performance. For $150 I think they are a great deal. They do some things better than HD580 but some things worse too. HD555's are more forward, exciting cans but can sound grainy and lose soundstage detail. HD580's are more refined, smoother, but more laid back. I think the HD580's are better for jazz, classical, and acoustic, but the HD555 is better for anything else. If I had to pick one phone I'd probably take the HD555.
Gsferrari I'm sorry you don't like the HD595
. Maybe you should get the 555 instead? $100 less, and sound very similar, at least from what Jan Meier said.