And I think that's the key. When I had both, I noticed some of the differences that others mention, but I also find that I hear things differently than others on occasion. This could very well be due to my tin ears or my lack of proper terminology.
However, I thought the main differences between the mk1 and mk2 were what I perceived as slightly more distance in the mids with the mk2 (i.e., the mids did not seem as immediate) and a slight bump in midbass (i.e., they had some good thump with rock). I'm not sure that these perceptions agree with what others have noticed. To me, these differences were extremely subtle.
And it felt like the mk2 would benefit from a good swift kick in the ass by a more powerful amp than the 007tii I was using. From my brief session with the mk2 and the BHSE, I perceived the mk2 as evening out in the areas noted above--sounding more and more like the mk1. Of course, that was under Meet conditions and for only a short time, but I tend to agree with Nate on this one.