if your primary use is movie audio, then mixing surrounds is really not an issue because most of the side and rear channel audio is "positional effects" in nature. For surround music, the speakers all should match as closely as possible so the instruments do not sound "different" as they appear in the other speakers (timbre matching). If you get a major upgrade for your L-R fronts, than try your existing speakers in a surround location and experiment with the results. After a period of use, you feel the surround speakers need attention, you will know what sound to look for.