5.1 sound problem

[cvrak]

HI,

I have an Acer Aspire 8930 laptop and I occasionaly use Creative SB Extreme, in order to connect the laptop in my Creative's 5.1 system, and my Sharp LCD TV. I choose 3/2+SW 5.1 from AC3 filter, the sound is ok.

When SB Extreme is disconnected and I watch a mkv movie with 5.1 sound in my laptop, I have problem with the sound. If I choose 3/2+SW 5.1 channels, I hear only the SL and SR channels, and nothing else. If I choose 2.0 stereo system I hear everything, but stereo instead of 5.1
At AC3Filter properties "panel", I see the green output VU meters for L, C, R channels but so sound.
Do I have to make some setting in BS Player?

Pls advise

Chris