What ever you buy you need speaker high level inputs.
The REL has a high level input. From your integrated speakers output, to the high level REL inputs via a SpeakOn cable with one end bare. The bare wire goes to you speaker terminals on the amp, as per instructions, Red right, positive, Yellow left, positive, black left or right Negative.
Then out of your bass bins, high level outputs to you speakers, binding post..
Happy hunting
Regards