In reply to:

if you were to bi amp your speakers,would that change the impedance?


It entirely depends on the specific design of the speaker and its crossover design. But I believe that the "nominal" impedance (i.e., the minimal impedance across the audio frequencies) remains about the same in the majority of cases. So, for example, when you bi-amp the M80, you should consider that the nominal impedance for each amp is still 4 ohms (Alan, please correct me if I am wrong here).