Optiplex 7010 DP->HDMI audio failed.

We have rolled out a number of Optiplex 7010s to our classrooms, attached to both a DVI Monitor and an HDMI television mounted on the wall.  In September they worked great, mirrored displays and all.  Somewhere in the 107 updates since Windows 7 32-bit SP1 one of the updates broke the HDMI audio connection.  Nothing I do seems to want to make it come back.  I just found out today that it is for sure in the Windows updates, not some other software we've updated along the way.

My question is, has anyone else had this problem and know what KB I should uninstall to get this working again?

Thanks ahead of time for the help!