akar,
i do not believe that Beyer currently makes the 600 ohm version of the DT770. however, you *might* be able to get the 600 ohm older version
here.
also, please check out this
thread which details tomcat's opinion on the
DT990 250 ohm vs. 600 ohm:
"I have compared an old DT 990 Pro with 600 Ohm drivers to my new DT 990 Pro with improved 250 Ohm drivers once, both driven by an Earmax Pro, and I felt the 250 Ohm model did everything better: its sound was more lively, more dynamic, contained more ambience information, had a larger soundstage, and more extension at both frequency extremes, whereas the old 600 Ohm model sounded a bit dull and less involving. The old 600 Ohm model looked rather worn, and maybe it was past its prime, I don't know . . ."
check out this more extensive
thread by tomcat from headwize:
"Compared to the new 990 Pros the old 600 Ohm 990 Pros are downright dull, with a restricted dynamic range and limited extension at both frequency extremes. They do have similar tonal balance, centering musical proceedings firmly where music happens to have its center of gravity - in the mids - but the 250 Ohm 990 Pro is far superior in every respect: it's so much more transparent, "airier", its faster and more dynamic, has far deeper, tighter and more impactful bass, and a treble that just sparkles, that is very much how violins, brass or cymbals are supposed to sound."
dusty chalk has both the 250 ohm and the 600 ohm DT770. dusty? . . .
