problem with rear sound (ultimate x64/asus maximus formula)

hi
i've built a new pc a few days ago and installed vista(ultimate/x64) for the first time. so far, so good, but my rear headphone jack doesnt work (anymore? im not sure, but i think it already did...). the rear mic jack works perfectly, so i suppose that the mini-sound card that came with my asus maximus formula isnt the problem. the front headphone jack works as well, so the headset isnt the problm either.
i guess, i configered the audio wrong, cause my headset isnt shown in the sound menu. but as far is i know, i cant add devices manually there. plus, i told vista not to auto-recognice the speakers/headset on startup ( you know, this annoying pop-up).

so, my question is where can i tell vista to ask on startup again?
or do you think its a different problem?

thanks in adance,
weinzey