Judging by the specs on the Cantons, it looks like those speakers like juice (88dB sensitivity, 4-8 ohm impedance). You would probably benefit by using a two channel amp for the fronts and maybe a monoblock for the center speaker. These three speakers see most of the action in a movie, and therefore are using the most power. Your receiver can easily handle the other 4 speakers (and probably the center as well). So yeah, I think that if your current receiver does all the processing and stuff you need and is only lacking in power, grab an amp or two for the front speakers.
Regarding bi-wiring/bi-amping. Bi-wiring is simply running a cable with a standard pair of connections on the receiver/amp side to the speaker where it splits into four terminations. People do this because they think the audio signals can split themselves into bass and treble frequencies and travel down the cable that connects to the tweeter posts and the woofer posts. I think it's absolute rubbish, but that's for you to decide.
Bi-amping uses an electronic crossover outside the speakers to send the treble information to one amp and the bass information to another. Then each amp is hooked up to its respective binding post on the speaker. This allows the amp for the treble (and if it's a 3-way speaker the treble and midrange) to be free of the large power demands of reproducing bass frequencies and therefore have more headroom. Consequently, since the bass signals have their own amp, they can play louder and cleaner.
You can bi-wire with any amp or receiver. To bi-amp with a receiver, you need a pair of extra channels. With a receiver like the Denon AVR-3805, this can be done by using the back surround/zone 2 amps. However, this limits you to a 5.1 configuration. Since you want 7.1, you'd need a receiver with 9 channels of amplification, and I only know of one that would fit the bill, the Denon AVR-5805. At $6k, I would think it's out of your price range. The easiest thing to do is power your fronts with external amps.
