A multi-party control unit (MCU) generates, based on audio data streams that represent sounds associated terminal devices, a mixed audio data stream. In addition, the MCU modifies the mixed mono audio data to steganographically embed sub-streams that include representations of the mono audio data streams. A terminal device receives the modified mixed audio data stream. When the terminal device is configured for stereo playback, the terminal device performs an inverse steganographic process to extract, from the mixed audio data stream, the sub-streams. The terminal device generates and outputs multi-channel audio data based on the extracted sub-streams and the mixed audio data stream. When the terminal device is not configured for stereo playback, the terminal device outputs sound based on the mixed audio data stream without extracting the embedded sub-streams.