My friend Joe pointed me to this Wired article on the sound of Death Magnetic this morning. I was interested to hear the Guitar Hero versions of the songs and found some FLAC versions online. I extracted FLAC versions of the songs off the CD, which I own, for comparison. I then opened the files for The End of the Line in Audacity.
As to what it means exactly, I can't quite say. You definitely have to turn the GH3 versions up more. In certain spots I feel like I'm hearing some new stuff. In All Nightmare Long at the 0:40 mark there's a sort of crescendo that is much more noticeable in the GH3 versions, for example.