I’ve written a small script that generate a graphviz graph from the information on /proc/asound/card*/codec#*. I’ve generated the graph for a bunch of different machines that have HDA Intel. They are interesting to see if you want to know what the hardware you have can do, and to find out the correct NID and commands supposed to be used by the alsa drivers. Here they are:

A Realtek ALC660 on an Asus W5F notebook

A Realtek ALC861 codec, found somewhere on the web

A SigmaTel STAC9200 on a Dell Latitude 120L notebook

A Realtek ALC880 on a LG LW20 Express notebook

A SigmaTel STAC9200 on a Dell Latitude D-something notebook

A Realtek ALC86x on a HP DX2200 machine

The script is on a GIT repository. You can clone it with:
git clone http://git.raisama.net/hda-tools.git.

What I would really like to see in the end is the ability to change the way the nodes are associated to alsa streams and mixers from user-space. Then this could be configurable using a GUI where the user would change the input connection settings and associate nodes with mixers and streams, while seeing the graph. Then instead of waiting somebody to change the Alsa driver to do what you want regarding the mixer and streams, you could simply change the codec settings on a GUI and everybody would be happy. :)