I have a un powered sub with 2 18s in it that is un powered. I have the amp that powered it in a movie theater. The sub has re

[Lantraw]

Movie theater sub with reg speaker connections to my new receiver with rca outputs

 

[Alabalcho]

Does your amp provide for sub-woofer channel? If so, is that channel powered or not?
Someone might help if you provide the model of your amp.

 

[americanaudiophile]

The sub out of the receiver needs to be connected to the input of the subwoofer amp that you got with the speakers. Speaker connects to that amplifier.
If it is a pro amp it may not have RCA inputs. If it has balanced XLR inputs you will need a cable with RCA at one end and XLR at the other or an adapter
http://www.mouser.com/ProductDetail/Neutrik/NA2MPMF/?qs=%252brH4t%252beVZ2M9YIPV8TVVTg%3D%3D&gclid=CKfp6p6frsgCFQcTHwod694AmA&kpid=96154546
Some pro amps have 1/4" phone plug connectors so you would need a different adapter
http://www.monoprice.com/Product?p_id=7149&gclid=CIzT2_SfrsgCFZCRHwodaSkAFQ&kpid=107149