Suggestion that I think is working: Google a video how to put v4 aircraft into v5 (primary with PMDG aircraft in mind). Then apply that method of installation to Milviz. Not perfect, but I think it works.
I tried your sugestion, it works partly, but at the end I get the following Error message '
"Prepar3D v4 found on this machine!!
XMLTools64.dll successfully installed in P3D v4 main folder !!
DLL.XML not found !!. Creating copy...
Cannot create DLL.XML - Folder not found !!
-Wrong User or folder corrupted. DLL.XML was not created.
-End of process-
Do you have any more sugestions?
The aircraft installs but some of the panel instruments don't