Please don't take the following the wrong way: did you triple check that your speakers are all in phase (+/- connectors)? It sounds silly, but it happened to me once (bad movement between speakers) and after wasting 2-3 hours of toeing-in, distance and levels... I decided to go back to basics and... ta da! The day before I had changed connectors on a cable; I had dropped the cable then picked it up; and then I properly connected +/- (based on the writing on the cable).... It turned out that the cable (not done by me) was inverted! So, as long as it was inverted to both ends, I was OK. As soon as I accidentally "repaired it", I was screwed!
So, this is probably not your case, but you may want to have another look to make sure.
