Preamp, Amp, Subwoofer

I have a nice set of monitors. I have considered adding a subwoofer to extend my lower range. To do so properly would require that I run a set of interconnects from the preamp to the subwoofer and then from the subwoofer to the amplifier. My question is, won't all of this interconnecting and introducing a crossover into the circut between the preamp and amp negate all of the research I did before purchasing my preamp and amp? Which by the I am very happy with.