Hi Din,
My *guess is that your assumption is correct on the DTS-ES question with 7 speakers, as that is how it works with my setup.
I too have been struggling with the 7.1 question: "is it worth it"? and, lately have been watching some movies (mostly LOTR) that send signals to some temporary speakers I have setup back there for the rears. I've had some interesting results, namely -- if I increase the levels in signal sent to the rears it seems to fill the room up more and accent some of the action scenes. Of course, at too much level increase it got to wierd, and distorted the intended sound track.
I'm really beginning to enjoy 7 channel stereo for music. And, for this reason, I'm going with the QS8's for the rears. (that would make my configuration: M60s, VP150, 4 - QS8, and the 350 Axiom sub) the QS8s are probably over-kill for rears, but I REALLY like the sound I get from my current QS8s, and think that more and more DVDs will be coming out to further extend the 7.1 expereince. (or, to get us all to upgrade DVDs and equipment.)
I recognize that there is some validity in putting direct speakers in the rears, but it probably depends on the room configuration. If you are hanging them on a rear wall -- then directs is probably the way to go. Mine are going on a side wall, about 10 more feet back.