Subwoofer connectivity question

I've got a lightspeed attenuator, a prima luna prologue 5 and a Parasound Z Dac.

What is the best way for me to hook up a sub? I was thinking if I could find a sub with RCA inputs and outputs, I could put the sub in line between the lightspeed and my amp. If the sub filters the signal so that its sending a high pass signal via RCA's, if I put in line before the amp, it would only be amplifying 80-100 hz and higher thus relieving some of the load of my amp in the process.

Anyways, what are your ideas on the best way to hook up a sub to this particular set-up (DAC, Lightspeed, Amp...)?

Thanks for your time and input!