When looking at power ratings of amplifiers, they are giving maximum power with particular levels of distortion (as the power goes up beyond the maximum RMS ratings, distortion levels tend to rise rapidly). The amplifier is NOT putting out that power always whenever you turn it on; the amount of power it is putting out at any moment is dependent on the input level (which, being music, is somewhat variable) and the position of the volume control. So an amplifier rated for 1000 watts may be putting out less than 1 watt, depending on the input level and the volume control setting. So you can use a powerful amplifier with speakers that cannot handle the total power that the amplifier is capable of putting out.
Basically, whenever the sound starts to become audibly distorted, you should turn down the sound. That, however, will not tell you whether the distortion is due to the amplifier reaching its limits, or the speaker reaching its limits, or both.
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