Two Sources to One Powered Subwoofer

I would like to know how to hook up two sources to one subwoofer. Right now I have a Sony STR-GX10ES two channel receiver with two rca outputs connected to my Quad Lite powered subwoofer. I just hooked my old Denon AVD-2000 Dolby Digital Surround Decorder and a Luxman F-114 three channel amp (to power the center and surround speakers). I then connected the left and right channel outs on the the Denon processor to the inputs intended for a graphic equallizer on the Sony two channel receiver. I have my source equipment (DVD player, Directv receiver and CD player connected to both the receiver and the Denon processor. When I want to listen to Dolby Digital, I use the adaptor switch on my Sony receiver and turn on the Denon DD processor and the Luxman and voila, I have 5 channel, Dolby Digital. That’s right, I said 5 channel, not 5.1 which is why I would like to connect my subwoofer to the Denon processor as well when I watch a movie or some Directv. But most of the time, I use the Sony two channel receiver when I listen to cds and some tv which is why I want the sub connected to the Sony as well.

Should I simply use two rca y-adaptor cables to connect to my subwoofer OR should I use an rca A/B switch, OR something else that I am not aware of?