I should have dug a little deeper... found this old thread by SoundHound (where is he, anyway?) with lots of good information.

I should explain what I think it might achieve. My VTF-3 has plenty of power and extension, but I find it more localizable than it should be. I also wonder if compressing bass signals from all six channels onto a single signal is costing me some detail, though it's just speculation.

My sub XO is set to 80 Hz (I'm using the 950's analogue for SACD/DVD-A -- it's a real help), and on some material the pull towards the sub is obvious. 60 Hz or lower would be better, but I can't do that on hi-res without an ICBM.

I visited Dr. Hsu once, and after he found out that I play organ, he fired up his twin TN cylinders on some nice, deep music... heavenly.

You both make good points about placement. I'm thinking of a symmetric setup, with L and R subs right next to the main speakers, and the LFE sub beside the listening position. At that point, the L and R should always add constructively because of identical pathlength (zero for the LFE, which will have a constant phase shift). I'll still have room modes to deal with, though.

Yeah... could be a lot of tweaking. Sounds like fun to me.