Two amps and two subwoofers, rca splitter isn't sending signal to both amps

[v7guy]

So I had a couple soundqubed amps laying around and a couple RE subs. Figured I'd run them both. 1 amp powering 1 sub, the other amp powering the other sub. Each amp is individually powered. I hooked everything up, put a splitter on each side of the  RCAs coming out of the head unit but only one sub will work at a time. When I swap the RCAs from one Y splitter to the other, the other sub will work. But they won't work at the same time. It's like the RCA splitter is only working on one side. 

Am I doing something wrong? Any help is appreciated. 

Is only one side of the RCAs sending a signal out from the headunit since it's a mono signal out to the subwoofer?