Sorry for resurrecting this thread, but I've recently found a site that I've found fascinating. It's
http://www.wendycarlos.com/gosurround.html, and it's got a lot of very interesting things to read.
For me personally, it made me try having my surrounds at 90 degrees for surround music. With my living room the way it is, those surrounds would be only four feet away, which is why I resisted for so long trying 90 degrees, but I decided to give it a whirl. I set 'em at 90 degrees, level-matched, then tried some m/c music, and sure enough, it sounded better than what I had before (110 or so degrees).
My surrounds are easily moveable, by the way, because they're up on bookshelves at 95 degrees. Whenever I want to listen to m/c music, I just bring them down and set them on stands at 90 degrees. Way handier than mounting them to a wall!
My mains were previously at 22 degrees. With Wendy's suggestion, I tried them at 25 degrees (a measly 3 degrees meant moving them a foot farther apart!). It ensured less of a "hole" in the sound field for m/c music, but I haven't noticed much difference for movies. I do wonder if the mains are now just too far from the HDTV for movies/TV shows. With the mains at 25 degrees, there's a space in between speaker and HDTV of about a foot and a half! That seems huge; I guess over the next few days of movies and TV shows, I'll get a sense if it's too big or not. Hey, it's all about the tweaking, right?
cheers,
supervij