I think when you look at the sensitivity of a speaker, the amplifier's watts are important but when you factor in the speakers low impedance, it becomes equally important that the amplifier can deliver adequate current rather than just power. For example, the old Quad ELS 57s only required low power (around 25 - 40 watts) but caused big problems for many amps that couldn't meet their current demands into their very low dipping impedance. I had many amps with the correct power ouput pack it in because they couldn't deliver enough current.
