Just to prevent any misinformation, note that power is not the issue. Tweeters, as an example need only milliwatts of power so adding a separate amplifier for a tweeter is on the silly side. The receiver has way more than enough power to do the job. And, as mentioned above, adding amplifiers that draw from the same power supply doesn't add any power. It only adds connections.
I don't know that it is the case in your case but the only potential problem is that of the receiver power supply being incapable of providing enough current for the impedance level of the speakers. As impedance decreases, current draw increases. Your receiver may be perfectly capable of handling the job or it might not be. That's a different issue. But biamplification won't cause it to handle a job it can't handle mono-amplified. That's a promise and a guarantee.
