Multichannel optical output unavailable (gray)

Multichannel optical output unavailable (gray)

Hello

I can not have an output multichannel audio in 5.1 (or 7.1) for the parameter digital output built-in "configure speakers" I stay in stereo.

Multichannel is gray

I am using the Apple DVD player DTS and DD 5.1 but

Why with the numérique optical output is not able to access the settings multichannel sound 2.0 digital audio output domme the parmetres Apple's program "audio midi"

xavier