bi amp imrpoving?

Are you referring to passive or active biamping? With active systems(which I've been implemented, at home, since 1980), your amps are only required to process the bandwidth assigned them. This, for instance, relieves the mid/high freq amp of the burden of reproducing bass, cleaning up it's signal and increasing dynamics. You can also use tubes on top, where they best perform their magic, and SS on the bottom, for the best slam, speed and definition. Passive biamping provides less in the way of benefits, but is much less costly, and easier for most to implement correctly(given identical amps with which to work). Articles on both methods: (http://sound.westhost.com/biamp-vs-passive.htm)(http://www.padrick.net/LiveSound/Biwiring/Biwiring.htm)

i mean to use one poweramp for the bass and one poweramp for hight and mid. it must be the active methode.

In that case, if properly implemented and adjusted, you can expect to hear significant improvement in practically all areas of sound.

If you intend to do active biamping, you must (1) bypass or remove the crossover built into the speakers and (2) implement a custom-designed line-level replacement for it. This is not trivial as off-the-shelf crossovers will not do but it has become easier lately due to computer-based modeling of speakers and crossovers.

Kal