Why not run a single RCA all the way to the back, and then do the Y splitter and go to the amps off the splitter? I would bet that your issue is somewhere in the mess of adapters.
You have two sub amps, do your amps have a pass through that you could use?
If all else fails, radio shack has every kind of wire splitter ever made... OR, you could wrap all the adapter connections in electrical tape. If they are the kind of splitters/adapters I am thinking of, they have exposed metal shields that could be touching something.