Subwoofer for 2 channel preamp

Buy two rca single male to two female adapter plugs(these are solid one piece gold platad, not y adapters).Plug the males into your preamp outs then connect your amp cables
and cables to sub line level in and use the subs crossover.

Thanks for your respond

I want to achieve the same thing too, but my component has a pre-out not a sub-out. Would I proceed the same way as suggested above?