Memory remap should be an option within the BIOS menu somewhere. Unfortunately MSI's documentation for your motherboard is the worst I have ever seen from any manufacturer, so I can't direct you right to it. They literally only show the top level Main Menu, and then the screen for the Cell Menu option, and nothing else. One more reason I avoid MSI....
Dual vs. single channel would only affect ram bandwidth available for the CPU. It would not stop the system from detecting one or more sticks. What is odd though is that your board only appears to have 2 ram slots, so if you populate both slots, dual channel should be the only option.
The only reason I can think of that it would revert back to single is if the ram sticks were of differing sizes, but that's not the case here either. Does the BIOS itself give an indication of whether it is running in dual channel or single channel?