If the speaker does classical music well it should do rock and jazz just as well, else it has some sort of rather serious flaw. It would only a matter of time before a classical recording would show up that flaw big time (try an original press of side 6 of Das Reingold conducted by Solti on Decca- if a speaker can play that right it will be good on any kind of music made). Trust me on this one- the speaker had better not care too much what flavor of music you listen to! As soon as it does, it is revealing its colorations/deficiencies.
BTW this is the same for all parts of the reproduction chain.
BTW this is the same for all parts of the reproduction chain.