I don't think I can help you myself
(I simply don't usually play 1080p mkv videos) but it might be helpful for your (and mine) fellow users if you post info on the audio-filters/codecs actually used by BS.Player for playback of the file. To that purpose load the file and then...
... (rightclick >) Options > Filters > Advanced
If you click on the [+]-signs in front of the codecs/filters shown you get further info
and access.
I suggest to post all audio related info (don't omit "source").
(P.S.: I'm also allergic for codec packs )