joema makes some good points. The success of a particular surround mix depends on both the material and the recording engineer's disgression.
Take the classic example of Pink Floyd's Dark Side of the Moon. This SACD is mixed so the images are far out into the room and fly all over the place -- but it works marvelously. A similar mix of almost any other source would fail miserably.
Most multi-channel mixes that I enjoy use the surrounds only to carry an ambiance effect, similar to what PLII does. These albums come across very naturally and I never really notice the surrounds competing for attention with the mains.
I've have several opportunities to hear PLII at work with 2-channel sources. When you first engage PLII, it takes a little getting used to, but when you switch it off again, the entire soundstage seems to collapse in on itself. Also, in my brief tests I preferred PLII to Logic7.
