Question about Optiplex 9010 AIO's & Realtek audio driver.

We have some Optiplex 9010's with Windows 7 SP1 that we set up in some rooms at the school I work at.  We installed the latest Realtek Audio drivers but the sound only plays through the speakers on the computer but not through the multimedia speakers in the room.  When I uninstall the Realtek HD Audio drivers in Programs & Features Windows 7 detects a High Definition Audio Device driver from Microsoft and the sound will play through the multimedia speakers.  Our RCA audio cables are plugged into the back audio port.  We have tried the audio port on the left hand side and the sound does work with the realtek driver on the  but for esthectics reasons we'd like to plug the rca audio cable into the back port to hide the cable.