Audio output setting on PS3?

[audio amateur]

I recently purchased a PS3, and since have gone through all the options and settings.
One of them I'm still not 100% sure on. My receiver is connected to the PS3 via optical toslink, and I am given 3 options for sound output from the PS3 using toslink:
-Bitstream (Direct)
-Bitstream (Mix)
-Linear PCM

Now I know that I am not to use PCM as that will result in only 2 channels of sound (albeit high quality i believe), so I have to decide between bitstream mix and bitstream direct.

Which should I choose and why?

[L.J.]

From the manual:

Bitstream (Direct) Set to output audio with the original digital signal prioritized.

Bitstream (Mix) Set to output audio that has been mixed with sound effects such as button sounds and then converted to bitstream format.

http://manuals.playstation.net/document/en/ps3/current/settings/bdsettings.html#1477

[audio amateur]

Yeah, id seen that before but it really doesn't say much.. What exactly am I missing with direct? It doesn't give any detail. Futher, why is there an option to choose between one or the other?