That’s weird indeed. Do you have a 5.1 system that you can test it on?
Yeah and it’s indeed weird 'cause all channels display something.
After a second check, it appears my sound system just “converted” 2.0 into 5.0, but it doesn’t sound anywhere close to the 5.1 of the bluray (if I put aside the compression factor, I just need to compare with Hal’s PT or Ady’s TESB which have 448 kbps sound tracks as well that really display 5.1).