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.
Become friends with Big.
Clear all 60 missions.
Get Level A on all the Action Stages by using Metal Sonic.
Get all 130 Emblems by playing Sonic Adventure DX.
Get all Emblems of the Chao Race.
Get all 130 Emblems.
Get Level A on all the Action Stages.
Get all Emblems of the Sub Games.
Get all Emblems in the Adventure Field.
Clear all characters stories.
Clear the Sonic story.
Become friends with E-102.
Become friends with Amy.
Become friends with Knuckles.
Become friends with Tails.