Is there a way to obtain IExplorerBrowser interface of running or newly open explorer window for subsequent BrowseToXXX call?
This isn't possible. See Raymond Chen's blog post on the subject.
Aha, the program is using Explorer as a “view this folder for a little while” subroutine. Unfortunately, Explorer doesn’t work that way. For example, the user might decide to use the Address Bar and go visit some other folders completely unrelated to your program, and your program would just be sitting there waiting for the user to close that window; meanwhile, the user doesn’t realize that your program is waiting for it.