I'm trying to hook my DVD up to my receiver using the optical cable. Is it supposed to be hard to fit in? I lined it up to where it looked like it would fit, but couldn't get the cable to go in. This is my first time trying to do this, so I'm not sure what's going on. Is this normal? I have an Onkyo SR600, and I bought Monster Interlink Lightspeed 100 Fibre Optic Cable.