My speakers (eltax symphony 6.2) say on the back that their impedance is '4-8 ohms'. Why does it give a range rather than a single value? Is it something to do with them being bi-wirable? Maybe it means '4 ohms if you bi-wire them, 8 if you don't'? I'm asking because my amplifier (Rotel RA820) says speaker impedance should be 8ohms or greater, and I want to know if it will work with these speakers. Apologies if this is a silly question, I'm new to this! All replies would be much appreciated.