bob katz book is by far the most advanced book i've found (with my limited research so correct me if i'm way off). most of the other books offer fairly obvious suggestions and therefore aren't worth the 30-60 bucks to me at least, but if you don't already own Mastering Audio get it now, it's definitely an intense read and for some (me) it took about the second or third time reading it to really grasp it all. Can't wait to pick up the 2nd edition, from gearslutz it sounds like he has added a few new chapters and updated a lot