Not just dipoles, THX is insipidly greedy. Funny you should mention the "Re-EQ" function. You'll like this. See, most engineers started remixing the movies for a home environment as the mixes would be too bright for the home and contain an "X-curve" that compensates for having to punch through a perforated screen. THX said "no, wait, that's altering the vision of the movie. See, you should pay us for THX movie certification and we'll *certify* that your movie is obscenely bright and harsh. Yeah, THEN we'll charge manufacturers to use our patented EQ for removing this harshness by rolling it off." And it worked, to a point. They did it. Of course, most movies aren't THX, only a relative few. BUT, it's just enough that having that function saves your ears fron being ripped off every once and awhile. A perfect example is Jurassic Park. WOW. It is BRIGHT. Even with DTS. THX processing sure helps out there. Too bad they got paid to create the problem and then got paid to solve it! True fact.
THX has three functions. It rolls off the sound of the fronts. But many processors have non-THX ways of doing this. It provides "decorrelation" which is a slight, nearly imperceptable dithering of the rear signals to give a *slight* stereo effect in the rears (PLII kicks the hell out of this) and an EQ to make dipoles sound more like directional speaker, which is impossible and therefore pretty useless. After that, it's just a "good housekeeping seal of approval". However, as we all know, THX doesn't mean it will sound good. Just that it meets certain specs. Many THX speakers sucked to high heaven and very few exist today.
As for what is best for 7.1, well, it depends on the processor. Meridian and Lexicon have sophisticated 7.1 processing. I am in the process of confirming how Fosgate does theirs, but apparently, if you set it to 7.1 speakers, it will automatically produce 7 different channels of info from Dolby Surround, Dolby Digital and DTS sources, even stereo ones. I'll be investigating further once my customers allow me to keep one in the store for more than an hour. Most preamps and most receivers can't do anything more than 6.1 so be prepared to grill the HELL out of any salesman who claims 7.1. If he can't explain how it's done, forget it, it probably doesn't exist. Most units simply double up on the rear channels so you end up with mono rears and stereo sides.
As to what sounds come front what speakers, here's how it SHOULD work and I'm trying to find a processor that does this. The processor SHOULD look at the left front, look at the left rear, then using a logic processor similar to what is used by Pro-Logic to turn stereo fronts into three fronts, it would derive a side speaker. The same would happen for the right side. Therfore, you'd have three front channels, stereo sides and stereo rears. The sides would provide a transition for any sound that was in common to or is moving between front and rear speakers. Who does it this way? Ehhhhh, working on that. However, done this way, you would get good stereo imaging front, side, rear, with more or less equal or potentially equal emphasis on all speakers. In this case, you would have two speakers to the sides, slightly behind the couch so no one is blocking the sound to the people beside them and two speakers at about 30 degress from the center line behind you. That puts each rear speaker about 60 degrees apart. You only want ONE speaker PER channel. 7.1 - 7 speakers, 6.1 - 6 speakers! If your receiver only does 6.1 effectively, you're better off with three rears, one behind you and the left/right rears at 60 degrees to the sides of the center rear. ANY time you have different speakers playing the same signal, you get cancellation effects which suck. That's another reason movie theaters suck. They stress "even" distribution rather than proper imaging.
Strangely, many processors send the "rear" sound to the sides. Or, they derive dual center rears in mono. Or they put the sound to the sides, then add ambience in the rear. All three are stupid ways of doing it.
If you want to read up a little more, I do have some more general info on my site, I have one piece I wrote on speaker setup in the advice section and a "Guide to Home Theater" under my newsletter/PDF section. Hope that helps.
John
