Here are some of the options you have with the RS wall wart:
1- this is my own setup, you would have to build your pass-through and atty adapters for this one.
2- faster to make with your actual setup, you only need to add an USB connector to the wall wart, and a regular pass-through with this adapter to be able to connect.
3- one more would be to cut off the USB plug on your pass-through and the connector on the wall wart, and solder one rca jack and one plug.
4- the fastest/easiest would be to cut off the USB plug on your pass-through and the connector on the wall wart, and attach one to the other, but then your pass-through will be limited to use only with that wall wart.
I hope all the pics show, they seem to come and go for some reason.