In audio, the speakers are much more important than the amplifier. You will not easily hear a difference between two good power amplifiers, but you can easily hear the difference between pretty much any two speakers.
As far as matching goes, you want amp power > speaker power handling. If the amp distorts before the speakers do, you're not getting the most out of the speakers, and clipping can be bad for some speakers too, especially tweeters.
Also, the THD figures quoted for amplifiers are usually at moderate output levels; they get worse with higher voltage swing. An amp that is getting close to clipping will generally have worse THD than one which is nowhere near clipping. (As well, THD gets worse with rising frequency.)
As far as matching goes, you want amp power > speaker power handling. If the amp distorts before the speakers do, you're not getting the most out of the speakers, and clipping can be bad for some speakers too, especially tweeters.
Also, the THD figures quoted for amplifiers are usually at moderate output levels; they get worse with higher voltage swing. An amp that is getting close to clipping will generally have worse THD than one which is nowhere near clipping. (As well, THD gets worse with rising frequency.)