When a headphone manufacturer releases a flagship, one would expect uncompromising sound quality, exceptional design and extreme comfort. As Audio Technica's current open circumaural top of the range model, the AD2000 comes off as a mixed bag. But it does have a big redeeming feature that has earned it a number of fans, and for this owner, it has charmed him enough to keep it together with the HD800.   It is the midrange which strikes the listener the most, it is a lush, forward midrange that suits female vocals to a T. Whether alto or soprano...