Check the speaker's impedance, sensitivity, and power handling. Start by making sure the amp is rated for the speaker's impedance. Many people tend to look at the power handling capability first, though when listening to music as opposed to test signals, this spec is not as important as it may seem. The higher the amp's capacity, the better, regardless of the speaker's power rating (without getting into extremes). A less powerful amp compresses signal peaks earlier, and speakers don’t like being fed with distortion from an amp that's always clipping because it's underpowered - this is a very common cause for speaker damage. Also note that the lower the sensitivity, the higher the power that's needed to produce the same listening level.

Other factors besides the specs:

If all channels are run through the preamp's bass management, less power is needed from the main amplifier. Bass takes up a lot of the energy in the typical recording, and bass management shifts a lot of this burden to the subwoofer.

Size of room - the further you sit from the speakers, the more the volume has to be turned up to compensate.