Samsung c5900 with External Harddrive

Hi All,

I searched around for answers to this but can't find anything. I have the Samsung 3D C5900 Blu-Ray player which I purchased as it has a usb. It states that it plays mkvs files but when I have converted any Blu-ray rip to that format it plays but will not play the HD audio just goes to either DD 5.1 or DTS. When I had a PS3 I used to plug in an external drive and it always played the HD audio, it also played avchds as well which this is supposed to. The player is capable of all HD audio. Am I doing something wrong here??

Thanks to all
ohmss