UPDATE! While waiting for an answer I was able to find out what this "unknown device" was, and how to correct the problem. Apparently, this is related to Intel's "QRT" (Quick Resume Technology) and can be addressed within the BIOS. To get rid of the issue, enter the BIOS (F2) at start up. Then go to the "POWER" tab. Then disable the Quick Resume Technology within the BIOS setting. We you restart this issue goes away. Hope that helps anyone else with this issue.
I have two of these boards and have always wondered this :-)
I've disabled it and the (?) has finally gone away in device manager, woohoo
I'm glad this helped you resolve the issue. It drove me nuts for a couple of days, too (LOL).