The dynamic range and ambient sounds on movie soundtracks can be a challenge for voice on most consumer speakers. These soundtracks were originally mixed and mastered for high end high $$$ professional movie theatre sound systems(which have much bigger dynamic range). Unless they have been re-mastered (compressed) for consumers or you have professional gear then you will often run into trouble with audibility of speech.
Basically, mid range compression and mid/bass distortion in most consumer speakers will disguise low level vocals...
Unlike music, where voice can be easily compressed to make tracks uniformly loud and audible, the intonation and voice levels of actors in movies varies greatly, after all this is natural and a huge part of expressing emotion/acting....a movie sound track that is highly compressed will lose much of its impact.
This is most likely your problem - it is an all too common one.
Basically, mid range compression and mid/bass distortion in most consumer speakers will disguise low level vocals...
Unlike music, where voice can be easily compressed to make tracks uniformly loud and audible, the intonation and voice levels of actors in movies varies greatly, after all this is natural and a huge part of expressing emotion/acting....a movie sound track that is highly compressed will lose much of its impact.
This is most likely your problem - it is an all too common one.