As far as the 5.1 and the 6.1 out there here is what I know(or think I know):
Dolby Digital 5.1 - Dolby Labs
DTS - which is a competitor to Dolby Labs
Both above formats are 5.1: Left Front, Center, Right Front, Left Rear, Right Rear, and LFE(some call it subwofer out(.1))
Then DTS came out with
DTS ES: Same at DTS with the addition of a matrixed rear center.
To counter, Dolby labs working with THX came out with:
THX EX also known as Dolby Digital EX, this includes a matrixed rear center channel. You will never hear Dolby Labs call it 6.1.
Then to one up Dolby labs, DTS came out with:
DTS ES 6.1 Discrete. This has a true encoded dicrete rear center channel, it is not matrixed.
In all formats the channels are full range with the exception of the LFE.
In Prologic(Dolby Labs): This consists of Left Front, Center, Right Front and Matrixed mono rear channel in a specific frequency range.
To sum up the formats are:
Dolby Prologic
Dolby Digital 5.1
DTS
Dolby Digital EX or THX EX
DTS ES
DTS ES 6.1 Discrete
I hope this helps. If I am wrong in anything above, someone please correct me so I can get the right story. This is what I think is out thee and my understanding.
Thanks
Mustang6
Covington, LA