enough amplifier power

russ69,

The reason for the twice as powerful requirement is for clipping.

Do you know what that is ?

If you overdrive an amp, it will clip and may actually DESTROY your speakers, typically starting with the tweeters first.

With and amp twice as powerful as your speakers however, you cannot quite do that even if you accidentally want to because you will notice your speakers getting strained (but not destroyed) sounding really bad and you will turn the volume down.  With clipping, you will not have enough time to react to turn down the volume.  Clipping happens almost instantaneously.

However, if you do have an amp which can soft clip (again, as I indicated above), then this danger is no longer there and any combination of speaker & amplifier can be used safely.

A good rule-of-thumb is: 10X the average listening power. If you listen at an average of 1 watt then you need 10 watts for sufficient headroom. 2 watts needs 20 watts. 3 watts need 30 watts. 10 watts average needs 100 watts! 50 watts average needs 500 watts! 100 watts average needs 1000 watts! 

So many things I agree with here, and disagree.  Having efficient speakers opens up so many more choices in amps.  I can drive my Crites speakers with the XA25(really 80W) to at least 105dB continuous without leaving Class A.  Clear as a bell.  Granted my ears can't take it but it sounds good.  Having subwoofers does help your amp breath easier.  So many variables here but I think it is more a mismatch of components than the sizing of the amp.  I don't see why you need a boat anchor megawatt amp with efficient speakers.   Not saying it won't sound good, it will.   There are many examples of efficient speakers and even more examples of nice amps so we all should be able to find a match.