I just put together the system listed below using a MSI P6N diamond motherboard. I installed the built in sound card drivers and the machine seems to play sound just fine, but there is no sound from the rear audio jacks. I have a front i/o audio panel installed and have that plugged into the motherboard and I get sound out of that jack up front. Does anyone know what is going on? I can't figure it out at all. Does plugging in front audio panel disable the rear jacks? I am confused and can't figure it out at all. I haven't unplugged the front panel to see if I get sound out the back, but will when I get home from work. Frustrating. Other than that, I have had no issues with this board at all. Everything worked as expected without any glitches other than this. It is a big glitch for me though since I like to game and I want good sound!
Some boards use headers to route the audio. Typically, you install jumpers to run the audio directly to the back bracket jacks, or instead connect "in" and "out" wires for the front panel jacks. If your case doesn't have both "in" and "out" wires for the front panel audio, the audio may be routed to the front panel, but never come back. Your MB manual should have details -- look for the front-panel audio header info.