How good is Dolby Prologic II, IIx ,IIz for downloaded movies and mp3s?

[bobby0909]

Hello everybody,

This is my first post in HiFivision.I have been a regular(reader) of this forum for the last few months and the information (first hand) provided here is huge.

I wanted to know the following basic things.

a) Is 7.1 surround better than 5.1 surround for movies and music when output through Dolby Prologic IIx & Dolby Prologic II respectively using a AVR?

b) How does Dolby surround sound stimulation i.e. Dolby Prologic II , IIx ,IIz stand against other surround sound stimulation techniques like Logic7 and others?

Thanks