As long as your nominally 6 ohm speakers don't have any dramatic impedance dips or peaks, I think the ARC's will do fine. Use the 4 ohm tap - it's better to mismatch the load on the high side of the amp output impedance rather than the low side. You'll effectively lose about 20% of potential output power.
Given the nominal nature of speaker impedance and output impedance, I doubt you'll notice any difference.
BTW Ralph - The equivalent circuit for the amp looks like am ideal voltage source in series with an impedance. This impedance represents the output impedance of the amp. It can limit current into low impedance loads since it is in series with the speaker.
Also, for those whose math is rusty, when dealing with alternating current (i.e. audio signals) the voltage, current, and impedance are complex quantities (i.e. each is in the form a+bi, where i = sqrt(-1) ). For impedances, the imaginary part is the reactive component, and the real part is the resistive component. Complex arithmetic models the energy storage behavior of capacitive and inductive elements in the circuit.
Given the nominal nature of speaker impedance and output impedance, I doubt you'll notice any difference.
BTW Ralph - The equivalent circuit for the amp looks like am ideal voltage source in series with an impedance. This impedance represents the output impedance of the amp. It can limit current into low impedance loads since it is in series with the speaker.
Also, for those whose math is rusty, when dealing with alternating current (i.e. audio signals) the voltage, current, and impedance are complex quantities (i.e. each is in the form a+bi, where i = sqrt(-1) ). For impedances, the imaginary part is the reactive component, and the real part is the resistive component. Complex arithmetic models the energy storage behavior of capacitive and inductive elements in the circuit.