Hi! I had the same problem with the headphones...Actually 2, one sometimes it wouldn't play the sound through the headphones, or when it did, the speakers would still be on. It's working fine now though. I uninstalled all VIA sound drivers, restarted the computer. Installed the VIA 10800 version, and restarted again. After that the audio was still coming out through the speakers. However for some reason, after running an audio application and restarting for a second time after the VIA 10800 driver, the problem was fixed...Not sure why, but hey, it worked...
SO far the best drivers I've ran were 10600 and 10800...10900 kept on turning off the equalizer (which is pretty much a necessity for this computer, if you're picky about audio), and I had to turn it on every time I switched applications. But so far I liked the 10800 better (specially because it fixed my issue...).
Oh, another tip...if your current driver version is working, do yourself a favor and DO NOT upgrade or downgrade. Why fix what isn't broken? That's what got me to have my audio problems the first time. Make sure you read threads on that specific audio driver before upgrade, so you know if there are any issues with it....