See my answer in your other thread.
Yes, you would only use one connector for each channel. With the adapter I suggested, that would be the XLR female.
I had looked at the manual for the amp before responding earlier, and it indicated that all four input connectors on each channel are wired in parallel. So probably the only reason that more than one connector would be used at a time would be if you wanted to connect a signal into the amp, and then connect that same signal from the amp to another component.
BTW, based on some blurry rear panel photos I saw on the net it appears that the "pin 2 hot" setting of the polarity switch, that I indicated should be used, is the position that is depicted in the drawing adjacent to the switch as having pins 1 and 3 connected together and to "G" (ground).