Problem with Sound on Headset

Hi guys
I try to use OpenPHT i found so many problems on Plex Media player… anyway
I have this problem i select a TV show, i hear the theme sound cristal clear , just perfect, but when the show start the sound is like in a cave , is terrible
all with a BH-503 headset (bluetooth) i must repeat when the tc show music intro plays is sound great !
I try with different shows
Any ideas ?
OSX 10.11.6
PMS last version OSX also

is audio output set to 2 channels in openpht?

Yes and i even try 2.1
The current setup is:
Channels 2.0
Audio Offset 0 ms
Output configuration best match (i try all)
Maintain original volume on down mix SET

And as i say before the Theme from the TV show sound GREAT is the sound on the TV show
Most of my shows are ACC (h264 and 265 video codec)
Because of the x265 i set the force transcode

The Theme music comes from a different source then local usually and is unrelated to the actual shows you’re playing. Can you post a sample XML of a problem episode and the Audio Output preferences you’re using?