Steve, regardless of what sort of receiver or separate amp you might use, setting it at a certain impedance(if it has such a setting)doesn't mean that you're "running" it at that impedance. As previous replies have said, the only effect of the lower impedance setting is to reduce the maximum voltage and therefore the maximum power available. You're not "losing" power by leaving the setting at 8 ohms; you're keeping the possibility of outputting maximum power, as long as the receiver/amp can handle it without shutting down. As to whether you actually need the maximum power which the receiver is capable of, that depends on factors such as your distance from the speakers, the size of the listening room, the dynamic range of the recording and your average listening level. It's entirely possible that you're not using all the power that you have now and that a slightly more powerful separate amp would be of no real benefit.
