Toe-in or NOT toe-in ??

IMHO. . .you need to try for yourself and see what it is about each that you like. In general,and at least for my own observations on this matter, toe in will focus images more specifically at the cost of narrowing your sound stage. Toe out will widen the sound stage. See what your own preferences are. (FWIW. . . my own speakers are about 8 ft apart toed in slightly (about 1/2 in), and about 5 feet from the rear wall in depth. Using Atma-Sphere MP3 and M60's, the sound stage is large anyway, so I prefer the added image focus).

I completely concure with the above. I have however, never owned or set up a pair of speakers that didn't benefit from some toe in and I've owned and set up ALOT of speakers. YMMV.

Vandermeulen and McFarland make sense. Aside from achieving a wider soundstage when speakers are towed out, things will usually sound more spacious. Towing in seems to reduce spaciousness somewhat, while giving the psychoacoustic effect of more centerfill. I find the most rewarding and enjoyable position places the center of my speaker drivers directly in line with the outside of my ears. I also ensure the distance between the center of the left and right drivers is the same as the distance between those centerpoints and my ears, thereby producing an equilateral triangle(the so-called "rule of thirds"). Of course, if your speakers do not have drivers, you will have to modify your approach to achieve your "ideal" placement.

When you hit the right angle of toe-in, you'll know it. Imaging will still be very specific, but the tweeter won't beam at you. I have had 2 pair of Spendors,(SP100 and 9/1) and their manual tells you to face the speakers directly at the listening position so that you don't see the sides of the speakers, but in practice, that was never the way that sounded most natural. Trust your ears.

It all depends on the speaker.
Opus, equilateral triangle setup and rule of thirds are not the same. Rule of thirds is dividing the room in thirds starting off the back wall.