how to downgrade an unknown (2005) interface name from SSIS 12 to 05 The namespace Microsoft.SqlServer.Dts.Runtime.Wrapper was research, but a suitable SSIS 2005 counterpart to a SSIS 2012 interface named IDTSConnectionManager100 was not found.
Any help for the concrete old interface name would be appreciated. 
Or do you know a kind of mapping overview / website for this kind of issue?
In SQL Server 2005, there is an IDTSConnectionManager90.  It comes with the note "this interface supports the SQL Server 2005 infrastructure and is not intended to be used directly from your code."  A very similar note is provided for IDTSConnectionManager100.

These two are not 100 percent identical, of course.

However, these are SQL Server version specific components and are intended to be used through the ConnectionManager class.  For 2005 see:

http://technet.microsoft.com/en-us/library/microsoft.sqlserver.dts.runtime.connectionmanager(v=sql.90).aspx

http://technet.microsoft.com/en-us/library/microsoft.sqlserver.dts.runtime.connectionmanager_members(v=sql.90).aspx