That's funny, I had completely the opposite experience with Rust in Peace, which is one of my favourite metal albums of all time. The original stereo mix is no great shakes, especially in the low end, but the Atmos mix seems to somehow make it worse for me. 90% of the instrumentation seems confined to the front, and it sounds really "small" and boxy as a result, and when the mix does employ the rear speakers it seems to be to pretty poor effect to me - guitar solos seem to occasionally wander aimlessly around the room without purpose or direction, while others are locked in the front center position and even occasionally too low in the mix, like Mustaine's solo at the end of Holy Wars. To me this mix represents either a failure of imagination or a failure of ambition because there are plenty of things you can do with multiple rhythm guitar overdubs, backing vocals, and twin lead guitars. What about having the Mustaine/Friedman call and response solos in Hangar 18 answering each other from diagonally opposite corners that switch each time they trade fours, have the backing vocals in Take No Prisoners come from the rears (or rear heights), have that crazy fast riff in Five Magics that comes in at 4:45 kick your ass from the rears, or have the disembodied vocal in Dawn Patrol emanate from the "voice of god" position in center height? There are tons of creative things that could have been done with this mix and I don't think the mixer took any of these opportunities.
