Here's a good and easy to understand tutorial by Rod Elliot:
http://sound.westhost.com/bi-amp.htm It starts with the basics and moves through both passive and active biamping.
It appears you want to add power. In this case you need to buy a separate preamp and power amp most likely. There's integrateds with alot of power but they are expensive. For well under a thousand it's possible to have 200wpc with a used preamp and amp. If I'm wrong and some other aspect of your system is what you're looking to improve let us know.
