Here is the full list of all 15 Sonic Adventure DX achievements. It takes around 40-50 hours to unlock all of the achievements on Windows.
Get Level A on all the Action Stages by using Metal Sonic.
Clear all 60 missions.
Get all Emblems of the Chao Race.
Get all 130 Emblems.
Get all 130 Emblems by playing Sonic Adventure DX.
Clear all characters stories.
Get Level A on all the Action Stages.
Get all Emblems of the Sub Games.
Get all Emblems in the Adventure Field.
Clear the Sonic story.
Become friends with Big.
Become friends with E-102.
Become friends with Amy.
Become friends with Knuckles.
Become friends with Tails.