Of course amps need not be matched to top end components, but to the speakers. The manufacturer provides a recommended range for their products. That said, if you want to simplify, a single amp can be used whether you connect all channels for not.
For instance, I have an active eq/xo system and use four amps (interconnect splitter cables) for each side of a two channel system. Since there is an amp for each individual driver, only 50-75 watts is needed per. The only 8 channel 50-75 watt amp I could find with decent specs was the ATI 6012 model which is 12 channels, 60w. Since I only used 8, the other 4 were unused. No problem.
For instance, I have an active eq/xo system and use four amps (interconnect splitter cables) for each side of a two channel system. Since there is an amp for each individual driver, only 50-75 watts is needed per. The only 8 channel 50-75 watt amp I could find with decent specs was the ATI 6012 model which is 12 channels, 60w. Since I only used 8, the other 4 were unused. No problem.