At first, I thought these weren't different enough from my DT880/600 to warrant the price difference (I got these for sub-$600, the 880s for $155). Gradually, I began to notice that these are more involving and seem to surround you with sound in a more realistic way. The instrument separation is fantastic. Keep in mind you need good sources for these to shine; FLAC files or well-mastered CDs (never tried an SACD so I can't comment). The 880s are brilliant, don't get me wrong. They are a neutral headphone that excels at electronic music (think Pantha...

  The AD900 is well known for its patent Audio Technica house sound; emphasizing light, airy highs. Separation of instruments is fantastic, but occasionally can cause the soundstage to sound artificially big. This is readily apparent when playing something like the Beatles’ stereo remasters, which have hard-panned left and right channels. While not common with more recent masters, this panning can be dizzying and fatiguing if the effect is strong or if one channel is favored. This is more a problem that stems in the studio, so I won’t hold it...