Hi Richard,
The amp debate is an ongoing saga and I think the reason is that everyone is correct. It all comes down to what you want from your system and how large a space you have it in. It is the logarithmic nature of power (both amp power and inversely distance) that makes it a bit confusing. If we use 15 dB as a safe range of dynamic headroom then in a small room at lower average listening levels the performance is highly likely to be indistinguishable between most amplifiers. For example; if you are seated 3 meters away from your speakers and you want a maximum average listening level of 86 dB then around 65 watts of dynamic power is going to work just fine. Since most receivers have the same continuous output as they do dynamic output a 70 watt per channel receiver is lots assuming it is rated with both channels driven broadband at less than 1% distortion. Now lets assume you are 6 meters away from your speakers and you want an average listening level of 92 dB. Now you will require around 1,000 watts per channel of dynamic power. This is where big continuous output with lots of dynamic headroom is going to be critical or your listening experience will be severely compromised. Since 1,000 watts of continuous power would require big mono blocks on separate circuits, the amount of available dynamic headroom becomes very important. A good guide to judging an amp's dynamic headroom available is found in the amount of storage capacitance combined with the type and/or sizing of the power supply. I have left a lot of the finer detail out here; but I think it gives the basic picture of what is going on and how everyone can be correct.
