MultiTerm Interop - Trouble with automated import of MultiTerm XML in Termbase

Hello community,

Every once in a while we get new MultiTerm XML files to replace our Termbases with revised versions. Since this affects 19 termbases, I am eager to automate this process. 
This means, I need to create a new termbase, use the previous version as template, and import the new XML. Rinse and repeat for 19 files.

Unfortunately, I cannot find the portion in the API documentation thatdescribes how to actually tell *which" XML to import.

This is what I have so far:

var multi = new Sdl.MultiTerm.TMO.Interop.Application();
var repo = multi.LocalRepository;
repo.Connect("Administrator", "");
repo.Termbases.Add(pathToPreviousTBVersion,TbName,"ReferenceTB");
var refTermBase = repo.Termbases[0];

var xdt = $"C:\\temp\\temp.xdt";
if(File.Exists(xdt)) File.Delete(xdt);
refTermBase.Definition.Save(xdt);

repo.Termbases.New(newTbName, newTbDescription, xdt, pathToSaveNewTB);

var xmlFile = pathToMultiTermXml;
var newTermBase= repo.Termbases[1];
var impDefs = newTermBase.ImportDefinitions;
var impDef = impDefs["Default import definition"];
impDef.ProcessImport(MtTaskType.mtScript);

From what I understand, MtTaskType.mtScript means "import without GUI", i.e. exactly what I need. Unfortunately, there is no method or property to tell the API the path to the XML that shall be imported. What am I missing?

Cheers,
Andreas