Creative MultiSpeaker Surround (CMSS) is part of the EAX technology supported by the Sound Blaster audio cards. It can also be found as a CMSS button on some multi-channel speaker systems and decoders. CMSS allow stereo upmix from various sources such as MP3, WMA, or Wav, to 4.1/5.1/6.1/7.1 channels, depending on your speaker setup and sound card model.
CMSS Music mode creates a convincing 5.1 channel surround soundfield from typical stereo sources, whether they are Dolby Surround encoded or not. It works well with Dolby Pro Logic, WAVE, AVI and MIDI program material. In essence, CMSS Music mode puts you "on the stage" for the music's performance, surrounding you with the performance.
CMSS Movie mode provides the sonic impression of being front and center at a movie screening. Dialogue and all normally centered sounds from a stereo program are heard through the center speaker. Use this mode whenever a music program has sounds you want to blend with on-screen action or dialog.
What is Upmix and how does it work?
The 5.1 to 6.1 Upmix works by deriving a rear center channel from the rear left and right channel. Illustrated below is the speaker output scheme for the various input sources: