YOU MUST ADD a crossover to feed the right stuff to each half of your speaker.
No. You must REPLACE the inbuilt crossover with the proper custom external one if you want proper biamping. This means that you must REMOVE the inbuilt on in the speakers in order to avoid cascading the two.
OTOH, you can leave the inbuilt one in place and not INSERT an external one but this will minimize any advantages of bi-amping.
You cannot use BOTH crossovers.
Kal