i have exactly the same problem.
2 channel sound but only to left ear.
On windows 8 64bit. Have updated to latest version of audio driver, 6.10 etc
Speakers work and get stereo but when I plug in headphones (good ones, NOT cheap ones), I only get the sound in one ear.
I have tried two sets of headphones and it happens with both.
This is really bad because this laptop was bought specifically to be used with headphones regularly.