Crossover upgrade capacitor question

Precisely matched smaller capacitors in parallel may work better than an equivalent large capacitor. A lot depends on geometry as well as the choice of dielectric. Remember that caps used in passive crossover see high voltages and therefore they change shape along with the signal flowing through them - this can add significant distortion in some cases and can affect dynamics. A better solution would be to go with active crossovers (using low level line signals) and consequently reduce this form of distortion and power loss substantially.