Take from Dolby's site:
Dolby Digital Plus
Dolby Digital Plus is a highly sophisticated and versatile audio codec based on Dolby Digital and designed specifically to adapt to the changing demands of future audio, video delivery, and audio storage systems while simultaneously retaining backwards compatibility with the existing Dolby Digital 5.1-channel home theater systems in use today.
Dolby Digital Plus is ideal for limited bandwidth environments such as broadcast television. As highly efficient video coding systems like H.264 are adopted, broadcasters can deliver increased capability and capacity through new set-top boxes in the same spectrum they are using today, while retaining playback compatibility with existing Dolby Digital A/V receivers. The Advanced Television Systems Committee (ATSC) approved a revision to the A/52A Standard (A/52B) that incorporates Dolby Digital Plus as the high-efficiency audio coding system for robust mode transmission of E-VSB. Dolby Digital Plus is also included in the Digital Video Broadcasting (DVB) specifications as an option for HD and other digital TV services. Devices equipped with Dolby Digital Plus are capable of decoding Dolby Digital broadcast bitstreams for compatibility with existing broadcast services.
This is sort of what I am talking about. 7.1 and 9.1 capable receivers are few and far between. Such as the Lexicon RV8 pictured here:
Like I said, when a movie is fimed and mixed in studio it is encoded with up to 9 channels of audio. Go to a movie theater, what do you see? Thats right, 9 or more speakers. These theaters utilize decoding software and equipment to fully exaggerate the ecoded audio. Receivers for your home would could cost thousands to do the same thing. I take that back. 10's of thousands. But most of the high dollar receivers like I just showed you will do 7.1. This is not some kind of beefed up 5.1 receiver like you would think. If a DVD has the capability to do 7.1 (which most dont) then it will do it.
You have to realize residential technology has not caught up to commercial technology yet. Hence the quote at the top of this post....hence the reason I say you will see it shortly...
Did that clarify it for you?