You can use a digital processor, as in a AVR, to separate the frequencies, or connect the speaker outputs to the subwoofer and the main speakers to the subwoofer, using the crossover in the subwoofer to divide the frequencies. Your manual should provide this information. Very few and very expensive floorstanding speakers can produce the low frequencies that good subwoofers can. Integrating the sub and monitors/floorstanding speakers is difficult without a proper crossover.
Subwoofer set up
How can I effectively use a subwoofer when my speakers go down into the range of the subwoofer. If the speakers are connected to the output jacks and the subwoofer to the subwoofer jack, both units will be reproducing the same frequencies at times. Even my bookshelves claim to produce lower freqs.