Hi David,
Sorry for the delay in my reply.
I own a professional type theatre fitted with 7.1 equipment. (2-front /1 x Sub/ 1x center and Sub/ 2 x side/ 2 x rear and all full range speakers / 2.5 Kw)
This is all in a a dedicated sound room approximately 8m x 7m x 2.4m
With this size room if you were to turn off, say the side channels you would notice a collapse in the surround sound field. Likewise if you turned off the rear channels.
Remember Dolby Pro-Logic? When left and right channels equal each other this would then form the center channel.Added to this was steering logic that placed the phantom image in the right position with the onscreen image.(Mapping)
The modern versions of this are DTS-ES and Dolby EX
As you can gather 5.1 which is the most common sound track on Blu-Ray is a serious compromise in my system where as 7.1 is great.
THX surround EX will map Blu-Ray 5.1 to 7.1 in all cases down SPDIF. No compromise.
When using direct full range analogue out from the Auzentech X-FI HD card 5.1 or 7.1 is all you get.(no mapping on 5.1 to 7.1)
I would like to see Cyberlink incorporate the THX surround EX into P-DVD-9 so that if your system is 7.1 you have 7.1 channels in all cases.
Trust this helps and thanks for your time. Thanks for bringing the no 7.1 analogue out to Cyberlinks attention. I suffer the same irritation.
Cheers Les