Whip, you're certainly correct that most music has relatively little content in the area handled by subs(say below 100Hz). The IEC 268-1 power spectrum standard(shown in the power rating section
here ), formulated based on an analysis of recordings of all types of music, shows an essentially equal requirement in the area from about 100Hz to 2000Hz. Both the bass area below 100Hz and the treble area above 2000Hz generally have a lower requirement. This of course isn't because upper bass and mid-range frequencies are inherently "power hungry"(see my above reply re this sort of misconception), but simply because there's more content and/or louder content in that frequency range.
Neither in theory nor in personal practice, however, have I experienced a "real challenge" in having a system that does an excellent job with both movie LFE(essentially all below about 80Hz)and the typically higher music frequencies. As long as the main speakers(whatever their size may be, whether termed a "tower" or "bookshelf")have good response to below the crossover with the sub, a smooth, continuous presentation results. With quality sub and mains(if they meet the required frequency response)both music and movie sound are enjoyed equally well.
