Hey Tim (And All),
It would really be fun if several of us started playing more with omnis. I have tapes as far back as 1991 that we did with AKG 462's, and a few years later we started playing with Gefell m296s and B&K (yes, B&K--you know, the good old days: )) 4006's.
While I'll have to look at how good my notes are from back then, I do remember noticing a surprising difference in sound quality when aiming them straight ahead versus "aiming" them at the P.A. Yes, with omnis, I did find that I liked them best pointed directly at the P.A. I apartently forgot this last week at the Mishawaka--it had been a couple years since I used them.
I have never used this "critically spaced omnis" approach because I'm still a bit perplexed by the concept. Omnis are only omni-directional up to about 5k. Above that they take on a directional quality. This would be one fun aspect to address when evaluating the best way to run omnis in our application.
Another consideration would be the spacing issue. Wayne is right on with his point that they need to be far enough apart to have separation but close enough to maintain a center image. Even at 4ft. apart, the recordings I made last week of Yonder Mountain String Band still suffer the "whole in the middle" (no center) syndrome.
Here's to some fun.
Happy Recording,
Marc