In as far as I know BSPlayer's subtitles do indeed not show under VMR-9. (You'll have to use e.g. overlay mode 1 instead). Perhaps this feature will be added when
bst has implemented renderless VMR-9 (at present still greyed out under BSPlayer's "Video rendering").
Do you need VMR-9 to play your movies?
Perhaps try the following "trick". Select VMR-9 and start up the movie. Then, while playing, switch to Overlay Mode 1. Does it do the trick for you?