This is on Intel DP45SG motherboard which has inbuilt Audio support.
It took me almost 3 months to figure out finally the quirks associated with IDT audio panel. I am not still very sure though, but just noting down the same here.
Task is to keep both headphone and rear speaker connected, but control those through the IDT panel.
STEP 1: Connect both rear and headphone jacks.
STEP 2: Open IDT panel from system tray. In windows 7, this is hidden near clock icon. Select Speaker option from left side and then go to settings page. That will show below screen.
STEP 3: Select Preference tab which will show below screen. In the end of screen, there is option to mute rare speakers.
I am yet to find a way to turn of headphone while it is still connected. The only way seems to be taking out jack. However this action destabilizes IDT panel when it is running in foreground. Hence, it is better to remove any jacks only when panel is in background.
Also, it takes this panel a while to recognize the jack inserted in front jacks.