Since most everything is encoded for 5.1 right now, I assume the extra 1 and 2 channels of 6.1/7.1 are just extrapolated from the existing surround channels?

I'm curious exactly how much information is sent to those extra channels. And in 7.1 are the 2 rear surrounds separate or just a dual mono output?

I don't know any more than you, but I believe they say there are relatively few DVDs currently encoded for discrete 6.1. The extra channel or two must be drawn out of the 5.1 soundtrack of most discs. They also say there is relatively little info that comes out of the rears in a 7.1 setup.
My question would be - with QS8s properly placed who would feel the need for 6.1 or 7.1? Pretty enveloping as it is, IMO.

I have read teh biggest benifit for 7.1 (or 6.1) is if you have a larger room. Because your two exisiting surrounds would be easier to detect where the sound is comming from, and thus the point of surrounds is just to add an enveloping sound.

There seem to be quite a few DD6.1 mixes. Not necessarily movies you would think would have a big sound track. For example My Wife got Calender Girls last night and it was 6.1. The amount of information sent to the rear chanel varies greatly from movie to movie. On many I don't hear anything from the rear and others really surprise me, never the movies I would expect. Without the rear speakers the rear sound is mixed into the surrounds. I don't find it that big a deal.

My experience with 7.1 (which I use) is that is "spreads" the sound out between the four speakers. Or I should say the left surround sound signal is spread out between the left surround and the rear left surround. What this means is that you won't get the full channels 4 and 5 signal PLUS channels 6 and 7, but you'll get a more split sound between the 4 surrounds. Perhaps, overall the same volume. But that only applies to matrixed 5.1 movies. With the quality of the QS8s it's not necessary to use the 7.1 setup unless for a few reasons. You want to have it for 6.1 encoded movies (the rear plays a mono signal), you want to use if for DD-EX movies in which there is special encoding for channels 6 and 7 (LOTRs and Star Wars EP 1 and 2 are good examples), or you have a large room and you want to spread the sound out. In my case I don't have a "huge room", but big enough that now when something comes from "behind" me it REALLY sounds like's it's behind and not side and behind. A great moment in movies is when Aragorn enters King Theoden's chamber in The Two Towers after he's been riding for days...they close the door behind him as he enters the room and it really is directly behind you.
So generally I'm an advocate of 7.1. Though in some cases, at least how my H/K receiver works, I usually like the sound of DTS 5.1 vs DTS-Matrix 7.1. There's subtle differences, but I think that my receiver is making changes to all the channels ever so slightly, and I don't care for that all that much.
So...there's my opinion on it all, for what it's worth

Are you refering to H/K's Logic 7 for matrix'd 5.1-> 7.1? I too am getting a HK 630 (tommarow!) and have read that Logic 7 does things very well.

Actually Logic 7 only works on mono, stereo and basic Dolby (non digital 5.1) signals. It does work well, but is unrelated to what is processed in DD and DTS.

hmmm, ok... so if you got a DD 5.1 source do the extra two channels get any information?

Yes they do but it's Matrixed.....at least on some DVD's I have tried. I'm still on the fence with 7.1. I had M80's up front with QS8's for surrounds and M22's for the EX channels and even movies encoded with EX didn't add much as far as I was concerned. I still think 7.1, 8.1 etc etc is more marketing then anything else. A good bud of mine went from a true 9.1 system down to good old 5.1 again and he is far happier.....I also did the same thing and have never looked back.