21" driver is not ideal but will work fine, what music do you play, more suited to deeper less punchy music.

To bi amplifer them you need an active crossover. This will split the audio signal in the required frequecies.
Need to make sure you match the Amplifiers ohm rating power to the relevent driver rating. Im sure if you go on the EAW site that will have what you need to know about required amp power etc.

Scanweb, not heard of but if is laptop driven its probally a LMS controller. Can bring up Eq and crossover slopes etc of laptop. If you get someone to set up correctly can probally save setting and then use in other places.
Probally has a limiter 2.

Have fun.