do the surround back speakers do they produce a different sound than the surrounds or are the four speakers just left and right surround . I dont notice any difference from the sb and the surrounds. All the dvds that ive seen are a 5.1 format does that ,mean im just getting the same surround affect from my surround back and surround speakers? I think the only way to get a true 7.1 surround is if you get an HD/bluray player is that correct?