Full orchestra and solo piano are the benchmark source materials for challenging speakers. Most can't hold up under the pressure, they weren't designed for it. If the speaker can stand up to those sources without stressing, without distorting, without sounding stuffy or wooly, and deliver the full dynamics, transients and bandwidth, it'll be a very special speaker. The best ones I've heard for this have always been active. I've heard some passives come close, but to really deliver, actives have a decisive edge. There are other important variables that come into play, but active is a good place to start looking.
