Most amps are able to make full power with just about any head unit. It won't make the amp any more powerful youll get the same amount of power either way as long as the gains are properly set. You just won't have to turn the gains up as far, which is a good thing because that is where a lot of noise comes from. It can be a consideration but i think its not a deal breaker on a new head unit if it has everything you want. You can always get line drivers to up the voltage coming from the head unit if it is a major problem. His speakers may just be more efficient.