Not to beat a dead horse, but I am a bit confused when you say I will only be using 10-20 watts with those speakers. Please explain. Sorry.
The efficiency rating on those speakers is 90dB/1watt/1meter. This means the speaker will output 90 decibels using 1 watt at a distance of 1 meter from the speaker. 90 decibels is supposed to be approximately the noise level of power tools or a blender at the same distance (1 meter). In order to achieve 3 more decibels the wattage must double. So we increase the power to 2 watts to attain 93 decibels. We double up to 4 watts to get 96 decibels, 8 watts/99 decibels, and so on. At 100 decibels is about the level of a chainsaw from a meter, and 110 decibels is unsafe if exposed for prolonged amounts of time, such as being right next the loudspeakers at a concert. So for high output the nominal amount of wattage use should be around 10-20 watts, with transients (drum wack, low bass from a synth, explosions).
Lower frequencies usually impose lower impedance and more power is demanded. The playback of a drum wack may take 50 watts when you are using only 10 watts nominally, but this is very short term. Truth be told, most receivers, even ones rated at 100 watts per channel, can't substain 50 watts continuous for long periods of time without stress.
