Is there a 'rule of thumb' when it comes to selecting how much amplifier power will be required to adequately drive a given set of speakers? One set of speakers I have looked at recommends between 20 and 150 watts of power, but most home theater receivers that I’ve looked at push 50 – 80 watts; which just seems a little weak. Are the speakers I’m looking at too big or the receiver too small; or is this normal/acceptable? Because I live within walking distance of a Circuit City I have looked at several Polk speakers, and HK and Onkyo receivers. Any thoughts?