I have the Asus P5B-E mobo and I had sort of the same problems. I also have 7.1 output via the on board SoundMax HD Audio. I have my Logitech Z-5300e computer speakers, my Onkyo TXSR503 via toslink, and some head set on the front panel. I ran into the same problem although I did get audio out of the front panel w/ no issues. The front panel mic on the other hand was a real pain in my ***. I would get it set to work w/ the front panel and it would work fine for a couple of minutes then just static. I would check the mic using SoundMax control panel and the audio recorder and nothing. So I would dink around, reinstall the audio drivers and then reboot. And what did you know the mic worked again, but only for a few minutes.
This problem was very aggravating, and I fixed it by plugging my mic into the back audio jack and not looking back. Try disabling the AudioESP feature, it automatically senses what jacks have a device plugged in and tries to set the devices up accordingly.
I know this wasn't any help, but maybe a little bit comforting that you are not the only one w/ this problem.
Let me know if you get anything figured out.
JuGgErS out.