Is there any reason why I should be using a Class D amp for my full range speakers, or are Class A/B fine? I'm not trying to enter any sound quality competitions.

 

Not really. Your amps will run marginally cooler with class D, but that's about it. If you were trying to wring every last mile out of an electric car you might think about the efficiency difference too but gas engines waste so much energy, it's almost pointless to consider efficiency of normal-listening-volume amp technology.