Since i had my new Imac 24″, i always had problems with sound card. I needed to patch alsa-drivers to make it works
Today i’ve tried the new Alsa drivers 1.0.16
and still no headphone sound, in ubuntuforums i’ve found a patch by nicfagn to make headphone work so i downloaded alsa-sources from hardy patched it and built a deb package.
This package make headphones and automuting work and it can be downloaded from here

I added the hardy heron version of the driver compiled against the kernel in hardy search for the post in the blog