Just wanted to say that the post from iMoron helped solve my sound problem, having just installed PCLinuxOS 2010.
I also only had audio from headphones and very quiet, noisy sound from the speakers. The solution was to add the speakers onto the Kmixer since it was only displaying: Master, PCM and Headphone controls! Why??
I dragged "Speaker" to the right panel, pressed the "OK", moved the slider up and voila .... sound, finally!
Hope this helps. And a big THANK YOU! to iMoron.