If you look at most modern speaker designers, very seldom (if ever) do they listen to, or use hard rock, pop or R&B as a reference. At most they will say that their speakers 'should' be good for it, but most often you will find that they have to use the best of the best recordings such as, Pink Floyd's DSOTM, or Dire Straits Brothers in Arms.
ZZ top and just about everything else that includes intentional distortion effects as part of that "brown sound" sounds good through those kinds of speakers. Imaging, mid range clarity, detail and neutrality with R&R music? From 3 or 5 guys in a band? It doesn't take much of a speaker to resolve that. It just takes the right one.
I have nice speakers, but when I want to bang my head, those bad boys come out. They don't care about room modes or recording quality and I can hear everyone in the band. Done.