The discs in db are version 2.0 of the game.
"Armored Core Master of Arena..Version 2.0 for PLAYSTATION..Copyright 2000, Agetec Inc" appears at offset 15D38 in the db dump (both disc).
On a version floating around the net "Armored Core Master of Arena..Version 4.0 for PLAYSTATION..Copyright 2000, Agetec Inc." appears at the same offset.
So somewhere out there is a version 4.0 disc.