I have a DP35DP motherboard with a AMD Radeon HD 6450 Display Adapter. I have been getting sound through the HDMI connection on the Video Card - everything seemed to work just fine. Recently I tried connecting a headset/mic and found that it did not work. After some research, I found, downloaded, and installed the updated sound drivers for the motherboard - and the headset/mic worked perfectly. but I lost the sound thru the HDMI port. I reinstalled the drivers for the adapter and the HDMI sound returned, but the headset/mic stopped working. I've tried using both the AC'97 and HD jacks on the motherboard (the case supports both) and still haven't found a way to get sound through both HDMI and headset/mic jacks at the same time. Does anyone know a way to resolve this and have sound through both? (the system is running WinXP-SP3)
The reason why you are getting this behavior is because the motherboard requires a video card, so the video and the audio are coming from it. The card does not support bifurcation.
The use of a video card disables all audio and video output coming from the motherboard. This board is an exception since it does not have onboard video.
The following link will provide you some recommendations for this kind of issue.
This is what I suggest you to do when you want to use the audio jack
Sound Playback is set to the wrong device
Go to Start > Control Panel > Sounds and Audio Devices, click Audio tab. Check the default device for sound playback; there can be multiple selections. Select the desired device, either rear panel or front panel.
Other solution will be to get a monitor or a TV with audio jack included.