interim fix for the crackly audio through headphone port.. in system prefs go to sound, on the output tab select headphones and move the balance slider to the left channel.. Sounds plays through both still and is crystal clear..
edit: after more testing, it seems you need to make some voodoo changes so i have uploaded mine.. Even when getting all the levels correct and changing the output nob in the voodoo settings it goes all crackly, then by simply clicking on the left/right slider in sound prefs it goes back to being crystal clear its loads of trial and error
but its important the sound app you are using in my case itunes is not set to full output or the bass gets overwhelmed.
On another note I found this online kext and will be working on it over the next few days
AppleHDA-2.6.0f1-ALC283.zip