Sound problem on Movies

Hi
I just bought a HiFi Rose
I connected my Rose 150B to an external DAC in AES/EBU.
When I play music from an external hard drive, it works fine. On the other hand, when I read a film on this same external hard disk (mkv), the image passes on television but I do not have any sound which leaves via my external Dac
My question is : Does the Rose 150 decode the 5.1 audio and convert it to PCM stereo in order to send it to the digital outputs Or does it just decode 5.1 and replay all channels (6) as PCM via digital output?
Thank you for your helping tips and experience

Thank you for your answer.
I would like to know if I download the VLC app, would it be able to convert the 5.1 sound to PCM stereo in order to be played by an external Dac ?
Have a Great evening