If memory serves me correct I believe when they started adding the back channels to theaters, it was a "sixth" channel much like DDEX 6.1 and DTS 6.1 surround and discreet which became available in HTS afterwards. Although the speakers were there, the people that made the movies and theaters never really advertised it. Other than DTS discrete which claimed a separate mixed channel, the back channel was just one extracted from the L/R surround channels.
In fact being a lover of gadgets that I am, between the time that 5.1 DD and DTS started to be available in AVRs and before they started adding the back channels, I purchased an item that was available for a relatively short time from the people that developed the "Circle Surround" format that you would add to your system with a separate amp and back speakers which, as mentioned above, extracted the sound from the L/R surround speakers. A more sophisticated version was available from this same company that was apparently used in many movie theaters to do much of the same thing. For all I know, it still could be the case. I guess you could say, when I purchased this little box, I was a "real early" adopter.
