Why don't you use the .bsi files??? See the ini_files.html document in the BSPlayer's doc directory.

Make one .bsi file for each of the movies and put these bsi files into the playlist instead of avi.

You can then define whatever you want for every movie - default audio stream, default subtitle, default font size, audio channels etc. etc. It is very simple as the .bsi file is the pure text file and can be simply made in notepad.