You're really looking for RMS watts throughout the power band, e.g. 20-20KHz, all channels driven simultaneously into a stated load, usually 8 ohms. In many good amps, that number doubles into 4 ohms. You should look at THM and IM distortion as well; these usually rise rapidly above the rated power, but that is of little concern if the power is adequate to your needs and the distortion base is low. You do need to read the fine print.
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