These new formats have names like Dolby Digital EX, THX EX, and DTS-ES. They originated at movie houses, adding a sixth or seventh speaker behind the audience to improve coverage. But homes clearly don't have the same acoustic needs. EX is especially problematic. Like Dolby Pro Logic before it, EX uses matrixing to create additional sound channels-in this case, a "back surround" channel served by one or two speakers. But formats like Dolby Digital 5.1 are far superior and vastly favored by most, because they provide dedicated center and rear channels.