Yes, I have the HD580. I re-grilled them with the 600 metal grills and got an Equinox cable for them. The bought the hd600 a few years later. They are so close that for me, I really wonder if I could tell the differences if I did not know which one I had on. A few months ago I got the HD650. I am a fan of the Senn hd6xx phones!
Because the music I listen to, and really the vast majority of all music simply does not have much of any content in the sub bass region (below say 50 HZ), this does not make me get very excited about differences in that range. I think that the next octave, 60 to 120 HZ is really more important in making bass sound "real" to me.
If one check the forums dealing with mixing, you will find that quite often they use a high pass filter based at around 40 hz when mixing for mastering. They know that the vast majority of systems don't handle much in the below 50 HZ range, that the human ear (even if some can "hear" at high levels) is way down in response at these frequencies. Therefor the information is usually lost, but yet makes the source work harder supplying the current, and causes drivers to labor (causing IMD) trying to reproduce information that most will never hear.
If you play music loud enough to "hear" 20HZ, through headphones, the rest of the music is probably damaging your ears!
Back to the comparison. The bass just sounds better on the 400i than the HD6xx, to me. It also sounds better than my HD400, Apparently this has little to do with sub bas capabilities. It has to do with things that I actually can hear at sane listening levels to program material that I use.
BTW, I am a fan of sub bass where appropriate. The home theater setup here will do in excess of 118 DB at 20 HZ. Gotta love thunder, explosions, earthquakes and sound effects.. even well recorded pipe organs in the proper venue. That is simply not what I use my headphones for. (except maybe very occasionally the organ stuff)