PS3-PCM Center Channel Setting

[ChiGuy]

I hope this makes sense...In setting up my PS3 audio, there is a selection for center channel voice to be used in PCM/Lossless settings. It states that this selection helps voices to be heard more clearly . What does this exactly do? If I select Lossless/PCM sound wouldn't this alter the sound from the center channel? To be honest I really cannot tell the difference having this option turned on or off. When I play a DVD with regular Dolby 5.1 settings through PCM, the sound is not as "powerful" as when I play it through bitstream. When I play a lossless DVD through PCM, it's about the same as listening to a regular Dolby 5.1 setting through bitstream. Does the PS3 center channel setting have anything to do with this? Thanks for your advise.