I have the same problem. After I removed a USB headset from my system, the line-out speakers, or the main two speakers. My subwoofer, rear and center speaker work fine, and are detected, but the front left and right speakers aren't being detected.
As you can see in the above picture, it simply isn't being detected.
Having a fair rage at my PC because of this. Wonder if anyone could help
The front jacks work, however, so it's not the speakers. Sound comes through fine on both headset and speakers through the front lineout jack, but it's just the rear.