My system was purchased in 2012 and I have a SW-110. I just upgraded my AVI and would like to add an additional sub. I've contacted Klipsch and they advised getting the
klipsch R-120SW Subwoofer connection to Old Audio Video Receiver VSX-D81OS | AVForums
Klipsch KSW-12 Powered Subwoofer SN # 12KSW-01360867- Black 743878028478 | eBay
Amazon.com: Klipsch R-12SW Powerful Deep Bass Front Firing 12" Copper-Spun Driver 400W Digital Power Subwoofer 14" X 18.5" X 16" : Electronics