OK, I know this has been covered in here, and I've searched and thought I made the right choice, BUT...
I just put in a Turtle Beach Santa Cruz 5.1 sound card (replacing a Soundblaster Live 5.1). Loaded the drivers. Seems to work, but when I just put audio into the center channel, it comes out of the left. I know what you're saying "the plugs are in the wrong jacks." I've tried every combination, and it doesn't do the trick. Something is screwed up.
I don't need a big high end sound card, I know my tracks sound good, I monitor through my Mackie HR824s through the whole process, until I start mixing to surround.
BTW: When I listen to a 5.1 mix through the stereo pair, it ALSO pans the center channel to the left side....
Internal bug?