Never mind 7.1, there is only ONE 6.1 format: DTS 6.1 DISCRETE. All the other modes are 6.1 channel with the rear centre channel being a matrix derived from the left and right surrounds. None of the other centre-surround channels have the discreteness of a true digitally-encoded channel. Now, as far as 7.1 channels are concerned, if splitting signals is all that is needed to "create" a new channel (and it flies in the FACE of the wonderful, discrete digital DD and DTS 5.1 we've now got and even the matrixed channels that are appearing) then why not have 4 speakers in the rear, and why not split the side surrounds into 2 each for 11.1 channels! The sky's the limit when all you are doing is adding speakers. Right now, the most "channels" you can have would be playing a Yamaha receiver, in DTS-ES discrete mode, overlayering it with Yamaha's own "upper front channels" for a total of 6 discrete channels, 2 matrixed and one subwoofer channel, for a total of 8.1 channels. I'm sure there are other companies working on even more elaborate systems. So, what you have here is three types of "channel making;" True discrete digital channels with wide separation and isolation such as DD 5.1 and DTS 5.1 and 6.1, Digital and "matrix" channel mixes such as DD 6.1 and DTS 6.1 non-discrete, and finally simply splitting outputs to add more speakers for a multi-speaker monophonic effect. Which has been done in theaters for years. The last thing is the possibility of the deriving of marginally discrete "information" channels by interposing things like a Circle Surround decoders between discrete digital channels. This was reported in Wide Screen Review magazine where the tester claimed to have heard isolated channel information between the normal 5.1 digital channels we now have with DD and DTS. I am not sure of the writer's claims, he seemed to think it was possible to derive SDDS (Sony's 8.1 digital discrete theatrical process) channel information from DVDs. Kind of wild. (Side issue: If we could have Sony's SDDS decoding at home, I would be in heaven simply because their theatrical digital is better than anyone else's) but it's worth messing around with since it's cheap. You can even fool around with old Pro-Logic receivers, feeding them two outputs (L-R surrounds) from a digital receiver and letting them output a kind of "center rear" channel effect by outputting from the Pro-Logic receiver's L-R surround and centre outputs. However, to preserve the discreteness of the digital channels, it would be advisible to simply use a splitter on the outputs, running one line to the Pro-Logic processor's inputs and one line to the normal surround power amps. The thing that separates "true" channels from fake ones are directionality and discreteness. If any matrix form of 6.1 (DD 6.1, DTS 6.1 non-discrete, etc) can actually do something like a pan across the rear three speakers, then it is directional. If the left surround and center image the sound, then the center and right surround do, then the centre channel is NOT directional because it did not really assist the panning of the sound. It merely functioned as a "fleshing out" apparatus designed to assist the L-R surrounds with their narrow dispersion, much like dipole or bi-pole speakers already do. THX used this "Hafler-esk" technique with Pro-Logic to achieve a crude and directionless "stereo effect" with Pro-Logic's monophonic surrounds way back when. They still use it to differentiate (slightly) your discrete L-R surrounds in new processors when "THX processing" is added to regular digital sound. It's a good thing humans cannot always link what's happening on screen with what sound is coming out of the speakers of THX's method would be very confusing. Secondly, channel separation with digital channels is WIDE. On the order of 80db or better. A matrixed channel is likely to have separation no better than 50db from the channels is was derived from. In this case, the centre surround is deriving the information it has from the L-R surrounds, with digital channels, the information is entirely "owned" by the each channel. The result is that matrix channels have the "bleed" we hear with Pro-Logic channels. Basically, information "leaks" into it from the other channels. The only time discrete digital channels have information in them that is in other digital channels is when the engineer encodes it into them. Do matrixed channels contain directional or discrete information? Maybe. My advise is to find out for yourself. Get ready to tweak your ears and CONCENTRATE like Hell. What all this means is that to get the best sonic quality out of these channels, you will have to experiment diligently with your system, adjusting levels, etc, to achieve the best result. Also, check out Dolby's website for a really good explaination for Dolby Digital EX and Pro-Logic II.