X-fi cmss-3d

I know that this feature upmixes stereo sound (like playing an mp3 in wmp11) which is why i have it permanantly turned on coz i have 5.1 speakers.

My question is, how does the cmss4d feature work when playing a game or movie that already plays in 5.1? For example if i play cod4 (cod4 is set to 5.1 in the games options btw) Does the cmss3d turn itself off?

I'd assumed thats what the 'Upmix:' option is for in the cmss3d control panel, so that setting it to 'auto' would disable it accordingly.

EDIT

Went on bioshock first with it disabled then let a big daddy walk accross the room so i knew how the 5.1 sounded. Then i loaded it up with cmss enabled & loaded the save & let him walk accross the room again - no difference as i can tell so perhaps it does disable it during games with a 5.1 source.