I am fairly ignorant about Sound cards, but I can direct you to a review about this card: TinyURL.com - shorten that long URL into a tiny URL
When you say "...the audio will only emit from the left speaker.
" do you mean that you are running this piece of kit as 2.1 channel, with sereo and a woofer, or more than 2 speakers? I ask because, although I am not 'into' gaming and PC sound issues, I did know quite a bit about Hi Fi sound once.
The Review states that the card uses 2 chips to provide sound to each set of channels, instead of the 1 chip as used by Creative. If, as you say, your card may not be seated correctly, this could cause your problem. Won't harm to check, if you are careful. My thinking, which may be wrong, is that one chip may serve right
channels whilst the other serves left
Also, note this from the Review: "... the Xonar DX still requires a power connector.
.." and this: " it’s a floppy connector and not a Molex...
I wonder if you made the right connections? Not doubting your knowledge or technique at all, but I have missed stuff by simply not reading the instructions carefully enough. Or not at all, sometimes.
That's about all I can help you with, hope you sort it and if so please post back with results, I am intrigued now.