a question regarding mkv and sound setup

[mediapc]

hi everyone,

As many will know, i have been months of headache with sound problems. I am using a gigabyte MA-GA78GM-S2H mobo and used to have the hdmi cable to output my sound to the tv.

Since I could never get the sound working properly, I have now decided to use an external amplifier with 3 front speakers and a sub (3/0/1 setup). These are being output from the mobo analog jack and directly into the amp. You must be thinking why i did not go for 5.1? Well because i forgot to feed the wiring under the carpet and to be honest i'm not too fussed about having rear speakers.

Now where i need help is setting up media player, kmplayer and zoom player to play ALL sound files via the 3.1 speaker setup, rather than stereo or DTS. Certain files such as .mov work perfectly, but .mkv files are missing the subwoofer base and i'm wondering how i can fix this??