Passive bi-amping as you describe will NOT double your power by any means, it will increase efficiency by simplifying the loads and should gain you about 3dB of headroom. It improves the sound more than the volume.
A bi-amping question
Right now I am using a Bryston 4B-ST for left/right channels in home theater. For center channel I am using an unmentionable monoblock. What I want to do is take my Acurus A125x5 amp that I have just lying around and bi-amp the center channel, using 2 of the 125wpc amps. Will this create the appropriate sound pressure level to match my Bryston?--or am I thinking about this the wrong way. Yes, eventually I will upgrade to all Bryston amps, but for now, I NEED to get the center channel level up. I do not like the result by boosting the level using the processor. The center channel is taking about 70% of the sound for movies and boosting it is just making it worse. For reference, I'm using B&W N804s for left/right, HTM-1 for center. These speakers matched for size, efficiency, frequency response and driver compliment. The processor (Proceed AVP) has only one center channel output, so I will have to find an IC splitter. Thanks.