I haven't played through it myself, but I helped a friend dial it in when he was testing it out, and we got some pretty badass sounds out of it. Took a few minutes to figure out how the preamps work, though!
Hell yeah man, its my first rack pre. Had to jump through so many hoops: from getting it, getting the 3 tube mod fabbed and installed, then had problems with the Mesa 2:90. Finally got everything working up to par and its sounding killer.