I'm guessing you either have Output Format disabled, or set to Source Number of Channels. If so, and you play a 4-channel source, then the output stream will, by definition, be 4 channels, and channel 5 doesn't exist in that 4-channel stream.
Try setting Output Format Channels to 5.1 or 7.1. Also select No up-mixing or down-mixing. Channels without content will contain silence.
Then, in Parametric Equalizer, use the Mix Channels function with the mode=Move to accomplish what you want. So for example, you would move Center to Left Surround.