I'm using Fedora, but I stumbled upon this thread as I was attempting to get my K50IJ setup, in particular I didn't have working sound.
As far as I can tell there is a bug/misconfiguration with the codec detection for this particular model, and to fix it I followed the advice in the following post: https://bugzilla.redhat.com/show_bug.cgi?id=509542#c3
So, first thing, what's HDA-Analyzer? Google turns up:
Basically, make sure you have python-gtk2 libs installed, not sure what they're called in ubuntu. Then running as root, might not need to I did in fedora, run the tool. You'll see a tree of 'nodes' click on Node[0x1c] PIN. Then looking about the display, you should see the section about 'EAPD', there will be a number of checkboxes as part of it, and one of those will be 'EAPD', check that one.
Then try out your sound, if it works, you're all set. If not, you might have to do a few other things, I did have to do the usual pulseaudio stuff like change the tsched=no, and reducing the timing from 25ms to 10ms as well.
I hope this helps. That last bit did it. I haven't tested the Mic or headphones. Best of luck!