If I understand you correctly you want to reliably trigger multiple builds of type A based on a list you pass to build B.
What you could do is have B parse the list (using powershell or whatever else custom program you want to use) and then use the TeamCity REST API to trigger builds of type A with the right parameters, the syntax described here would apply to this:
To trigger a build with custom parameters (system properties and environment variables), use:
http://testuser:testpassword@teamcity.jetbrains.com/httpAuth/action.html?add2Queue=bt10&name=&value=&name=&value=
This allows you to pass the parameters you need for each build.