You can bi-amp your fronts if they are bi-ampable; you can't bi-amp just any old speaker. You can tell if it is bi-amp ready if it has two sets of binding posts, connected by a jumper (you remove the jumper to bi-amp).

My mains are bi-amp capable, but my center is not. Centers don't usually have big woofers in them so I'm not sure that there would be too many out there that can be bi-amped. I haven't decided if I'm going to bi-amp the mains, yet, but it's definitely a down-the-road project if I do.

Also, those of you who do bi-amp: do you use a crossover in the signal cable to the two amps, or do you use a Y-adapter and let the speaker's crossovers do the work?