For the audio quality on the Thin Client the integrated VC Framework VC is responsible.
Therefore, you should disable the audio hardware support.
There are several ways, depending on which Citrix connection you use:
1. Session- Citrix XenDesktop/XenApp - Legacy ICA-Session- Sessionname- Optionen - Audiotransfer
or
2. Session- Citrix XenDesktop/XenApp - Citrix StoreFront / Web Interface - Optionen - Audiotransfer
