Note the following. It shows a HD Audio pinout compared to a AC'97 pinout. Sounds like your front panel of the case is using AC'97. Your motherboard only supports the newer HD_Audio.
I do not know if a front panel wiring from the case designed for AC'97 will work properly with HD Audio. Your case may also include two different wiring harnesses.
http://home.roadrunner.com/~expertpc/toms/f_audio.jpg
Notice how closely what you describe fits the AC'97 pins!
Note the above graphic and instructions are NOT about your motherboard.