A reviewer wrote the folloing. klipsch ksb-s1 surrounds "These are excellent for Dolby Pro Logic surrounds. However, they are NOT for Dolby Digital due to the limited frequency response. And, if I ever upgrade, what the heck am I gonna do with speakers that only reproduce 120Hz-8kHz?" Is this true ? And if so what are the frequency requirements for speakers to reproduce dolby digital and is that the same for all channels ?