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.
Get Level A on all the Action Stages by using Metal Sonic.
Get all Emblems in the Adventure Field.
Get all 130 Emblems.
Get all 130 Emblems by playing Sonic Adventure DX.
Clear all 60 missions.
Get all Emblems of the Chao Race.
Get Level A on all the Action Stages.
Get all Emblems of the Sub Games.
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.