So I have the Xonar DX and this is my first sound card. I installed it and attempted to play around with the settings in the Audio Center but the only thing that happens is audio comes out either left or right ear. Not sure what to.
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Ok can you try any different set of speakers/headphones/earbuds on it? This determines the problem is the card. The next thing I'd try is disabling onboard audio in your BIOS, from there I'd reinstall the drivers - make sure you get the new ones from ASUS's site. Let us know how it goes, it's worth these steps especially if you're using headphones thanks to the amp'd up output. This is the cheapest card I could find that will actually output 4.1 audio and works great.