I had the same problem, i finally solved it today. Here, i'm listing below, what i did.
After couple of unsuccesful research and tries, last 2 days;
First, i should tell i' ve done every combination of settings on realtek audio manager, i guess, none of them were useful.
Last, the solution part for me;
In bios advanced settings->onboard configuration i choosed ac97 for on board sound.
When i called the reseller, they told me that the connection between front panel and motherboard, isn't made. So i take apart the case, and checked the connection, there was a cable from front panel to Asus Xonar (external sound card) NOT to Motherboard.
So in device manager, i deactivated all sound devices but Asus Xonar. Then, i run "Asus Xonar Sound Manager" from control panel. Under "main" section, there is a choosing for input. FP Headphone. I choosed it, and woola sound is on front panel through my headphones. 🙂
Hope this helps.
Cheers,