I have a YST-SW010 powered sub that I want to connect to my Insignia NS-STR514 the problem is that my reciever is only 2 channel. Also I was wondering if I could use a Single RCA cable to bare wire to hook it up
It's not a dumb question. The answer is maybe.
That adapter is made to connect one output to two inputs. The reverse of what you need.
The problem is you don't have the resistor to isolate the two output channels feeding into each other. Sometimes that screws up the source.