An active crossover is a requirement, and it can be solid state or tube, depending on your preferences. Tube amps are less efficient than solid state, mainly because of the filament power needed. This is no big deal for me, but you have to answer these questions for yourself. The most used setup is a solid state amp for the woofers and a lower powered tube amp for the tweeters (the high frequencies need much less power - roughly half as much as the woofer or less).

Again, I would suggest you visit the Elliot site and others for detailed descriptions on what is needed to implement a setup such as this.