If you biamp or triamp, there's generally a crossover module used in the amplifiers (one for each frequency range) to force the frequency to the correct drivers. If you biwire or triwire, the internal crossovers are still used. I'm not sure how you bypass the internal crossovers when you bi/triamp, but there's a way to do it.

Bi/triamping is ridiculously expensive. For instance, for my Linn 5140s, I'd have to have 6 amplifiers and 6 active crossovers. For my center channel, I'd have to have two amplifiers and two active crossovers. It's not worth it to me. I'd rather just have two amps to each speaker and let the internal crossovers do their stuff. Or, have one kick butt amp that goes to all of the inputs on each of the front speakers.