no, the straps connect the two pairs of terminals, all you have to do is hook your speaker wire to either the bottom OR the top pair.
When you say the sound is coming from the center only, are you talking about music or HT applications. For music you should be using one of the Stereo modes and there would be nothing coming from the center channel. What do you have the receiver set on? Unless your listening to multi channel music would you be using the center speaker.
For movies the center handles most of the voices or dialog, which is normal.
