Gain Matching of the amps should be the concern if you don't want gaps between the upper/mid base/high end and the lower bass drivers. If the speakers have internal crossovers that can't be bypassed then you are stuck with using the internal passive crossovers, which isn't a real problem. Just remember that passive crossovers typically will have more losses. If the speakers have crossovers that can be bypassed or taken away altogether, then you can purchase an electronic crossover and have a good time biamping. Understand that most if not all speakers have in their crossover networks some wave shaping/wave correction circuitry to correct for issues inherent with any speaker. Therefore, before you buy an electronic crossover, please contact your speaker manufacturer and ask if another manufactuer's electronic crossover would work well with your speaker of if they sell an electonic crossover for your speaker. Typically, biamping you would want matching amps or if your crossover network (passive or electronic) comes with gain matching circuitry or switches, you can match the gains of the amps and there you go. it is relatively simple and the instructions are typically clear on what to do. So, it really isn't rocket science and doesn't take a masters degree to do this. Follow the instructions provided or ask the manufacturer. Depending on the speakers and the sensitivity of the speakers, this will help determine the power level required of the amps. but say you already are using a particular amp that you really like, then when biamping, just go get the same amp and have fun.
enjoy
