I feel like an idiot trying to hook up my first ever surround system (and first new receiver for more than 20 years). I have the Pioneer Elite 21THX receiver and I am having trouble connecting the speaker wire. I have followed the directions of stripping the end of the wire; twisting the bare wire together; loosening the connector on the back of the receiver; placing the bare wire in and then tightening the connector. Having done this, the wire is still loose and could be easily pulled out with little effort. What am I doing wrong?? Thanks.