@1982luca I dont think I am following, are your questions is clear enough for us to understand. The DCS API is the same endpoint used by the ID Sync service. When you say AAM API, are you speaking about the pixels you can fire?
The Audience Manager REST API is to interact with the actual tool versus to UI. Like to create segments, traits, to pull performance data for segments and traits, and etc. It isnt use to onbooard user data as an example or to do an ID sync, or to pull data about a specific user.