You certainly can connect them like this. But, it will only work on certain presets. If you use a "mono in, mono out" preset, or a "stereo in, stereo out" preset, you will only get one of the outputs.
To get what you want, look in the Preset Manual for presets that either say "mono in, stereo out" or "summed in, stereo out", or "switchable in, stereo out".
