Microsoft has released an update for Microsoft Windows MultiPoint Server 2011

Install this update to resolve issues that occur when a PS/2 station is configured on a system that has multiple non-USB audio devices installed. The issues may include the absence of audio on the PS/2 station’s audio device, or the audio from the PS/2 station’s session is connected to an audio device on another station. You should consider applying this update under both of the following circumstances:
You are using a PS/2 station with associated audio devices that are connected to the audio jacks on the computer chassis.
You have multiple physical or virtual, non-USB audio devices installed on the system.

Note:
This update is cumulative, and also includes the update discussed in the following KB articles:
KB2530453, KB2542222.

  Update for Microsoft Windows MultiPoint Server 2011 (KB2556903)