It wouldn't actually be more power, unfortunately--for one thing, it's all coming from the same power supply, and for another, even with separate amps, the power doesn't sum (tweeters and mids take much less power than woofers, so they'd consequentially be using a smaller percentage at any given volume level.)
The jury is out on "the more power the better" thing. Or, I should say, there is intense disagreement on it. But I don't think you'll get a lot of disagreement that biamping internal to the receiver doesn't give you more power.
