This is the arrangement for the REL sub I have, but most people want to use the sub's crossover. In this case, you have to run the amp output to the high level input on the sub, and then out from the sub to your speakers. In the case of amp>speakers>sub, you would only use the sub for very low frequencies, to augment the full-range speakers and use the sub's crossover to limit the upper frequencies from the sub. I need to know more about your system to answer your question.
