I find surround useful only when the surround channels are turned way down in level so that they aren't directly noticable; ie. I only notice their absence when I turn them off. Otherwise its way to gimicky & distracting. Movies or music.
Dolby PLIIx can be nice at low levels for the rears as long as you don't let it mess with the stereo pair, it's a matrix decoder, sort of a fancy version of the old Halfler circuit..
Anyone with two extra speakers and some speaker wire can play around with a simple 'ambience extraction' technique by wiring up a rear pair across the positive L & R terminals of the stereo amp so just the difference signal goes to the rears, with the surrounds wired in opposite polarity. No level control this way though so use less efficeint surrounds or point them at the back wall or ceiling. It's cheap and easy fun even if not for critical listening. Sort of a M/S encoder. It can be quite enlightening to listen to the difference signal for different sources if nothing else.