In the Lynx Routing page, there is a monitoring mode button. The default is stereo, so that a stereo source is sent directly to a pair of outputs. If you are monitoring a mono source, you should set this mode to either "Right Channel" or "Left Channel" as appropriate. When set to "Left Channel", the signal from the left Line Input will be panned to the center of the stereo field. Likewise with the Right Channel when right is selected.