I'm using 5.1 surround sound and my hp 2159m monitor the sound is distributed evenly through all speakers (left,right,center and sub). I recently changed my monitor to a 32 inch Sony Bravia KDL 32S2000 and now I'm only hearing sound coming from the center speaker. I checked the speaker config in the playback tab and the settings are still the same so it must be something to do with the monitor.
Well, how have you connected the 5.1 Surround to the rig?
What connectors are you using with the 32'' Bravia?
And what is your default playback device?
If it has changed to HDMI, you need to change it back to the Sound Card that is connected to your 5.1 System.