I just happen to be working on alsa for some Intel based HD Audio systems. That particular sound component was added to Alsa 1.0.10 (I believe). It is in 1.0.11 for a fact (what I'm currenty working with).
Go to
http://alsa-project.org and download the driver, lib, and utils. Build and install all three and you should have good 5.1 surround sound working (the rear line in and mic in jacks can be retasked to rear and center/LFE).
Good luck.