It's been awhile since I've done any A/B tests, so I just spent about ten minutes going back and forth between the Cowon and the 801 with the track "Coast" from Devin Townsend's album Ki. I used my Denon NC-800 headphones. I had the Cowon set to my preferred settings for the NC-800 which is a slight bump in the bass and lower mid to fill in the bottom a bit, and the "stereo enhance" at level 1 for a bit of extra width to the soundstage, which the NC800 can use. I tried the BBE enhancement off and on at several levels, and found that overall the sound was worse with it turned on. It completely eliminated any depth and most of the width of the stage, and made the mids sound muffled. The highs were perhaps a bit more present, but in no way more clear or detailed. I suspect I simply heard more of the highs because the mids had been cut. Ultimately I left the BBE off for my test. The NC-800 is a well balanced and pleasant sounding phone, and the sound out of the S9 was perfectly acceptable and enjoyable. It was not the trainwreck of the DT880-32 by any stretch.
Then I switched to the 801, and was surprised at how much better the NC-800 sounded. I remembered some differences, but not this much. The NC-800 is by no means king of anything, its performance is better than the ES10 which is a bass monster and not much else, but the DT1350 is definitely better than the NC800. Out of the 801, there was more width and depth to the soundstage, bass was more present and considerably better defined (and this is with EQ boost on the Cowon, and the 801 flat), the mids gained warmth and detail, and the separation of instruments was WAY better, with each clearly defined rather than simply a blur from the Cowon. The highs I actually thought had the smallest improvement. The NC800 to my ears is a bit rolled off in the highs, not dark like the ES10, but a bit sweet. It's high frequency resolution isn't exactly world class, and I suspect that the NC800 is the limitation there, not the 801. Still, the highs were a bit more present compared to the Cowon, and slightly clearer and better defined.
I want to make it clear that in no way does the 801 sound like it is down 2 or 3dB at 11-13kHz compared to the Cowon. That may be what RMAA says, but I'm not hearing it.