hnmmm im sorry but cant see th point in having speakers behind you.... at the end of the day, if u were to go to a music concert you stand or sit and look at the band with them infront of you, and the sound travels from them to you from infront not behind....
you go to the cinema, they have speakers set up so the sound comes from the front mainly with a good amount from either side of you and a tiny amount from the rear so that affects such as say a helicopter that would fly from the front to the back will give that effect...
unless you are listening to effect tapes, or have a screen and 5.1 sound... i dont see the point in having rear speakers, i mean even your ears are angled more forwards then back, so there is not a huge amount of point to rear fill.... if your components are set up right then you dont need rear fill, and that doesnt count for subs... as the human ear cant tell where the sub sound levels are coming from...