hi guys.. i neted a little bit of assisstance...... i am tryin to hook up a powered sub to my receiver, but the receiver does not have a sub output

wat i did was just coonect one rca to one of the PreOut then straight to one of the Line In Right at the sub... it does work, but the treble also comes out from the sub too, which makes the low frequency of the bass very distorted.... what i need is only the bass coming from the sub

here is the pic of the back of my receiver and the back of the sub thanks alot


SUB


RECEIVER