I've recently reinstalled windows XP on my PC and I'm having trouble with AC3.

I watch MKV HD videos with 5.1 surround sound using media player classic. While trying to set up AC3 to play 5.1 correctly I've come across a strange problem. First I double checked the audio track on the video by right clicking a selecting properties, this confirmed 6 channel audio (on more than one video). So when I go into the AC3 filter settings it says the input is only 2.0 and the output is 5.1. As I'm sure you are aware this is far from the effect of true surround sound.


Is there anything I can do to make AC3 detect the input correctly?