No audio from dvd isos with PCM

[bulmers]

Ive got a premium with an internal HDD, Ive transferred a good few dvd isos (all music concerts) to the HDD via filezilla. They all play fine with audio except the ones with PCM audio. I used DVDfab to rip and convert the dvds to iso. The dvds that work show AC3 audio in DVDfab and the ones that dont work show as PCM audio in DVDfab. Does anyone have any ideas on how to remedy this problem or is it a firmware issue?

all the best,
bulmers