they are quite efficient speakers (90db), which means they will sound quite loud for a given input level.
So you could use them with say a 20 watt amp and get reasonable sound/listening levels, room size and your preferred 'listening levels' will have some impact on this! The important part is not to overdrive the amp, this will cause 'clipping' which is not good and can quickly damage a speaker, especially tweeters.
The given power handling for a speaker, is in real terms, more of a guide figure, you could for example run them with a 100 watt or even 200watt amp, but just keep the volume control in check.
In short, don't overdrive the amp, don't overdrive the speakers!
Just use some care and if you start to hear distortion then ease back on the throttle.