Posted this a couple of years ago:
I’m just going to go at this as I’ve practiced it many times.
Normal front speaker set-up. Take long single wire from Rt (+) to Rt rear (+). Repeat same Lt side. Connect both rear speaker (-) terminals with single wire.
If anyone sees this as wrong and wants to scream foul, then proceed. As explained to me it provides out of phase material diagonally. So Rt speaker out of phase material appears in Lt rear speaker, same with Lt speaker material.
I’m no engineer, have just set it up multiple times with success. It broadens and deepens the soundstage.