I have two amps. I'm using a BOSS ES-8 loop switcher that has two outputs. Both outputs used to go directly to the amps. Now they go to the H9, and then to the amps. I think what I'm looking for is to "preserve the stereo image" even when that image is only one side coming through.
If the H9 has a mono input and stereo outputs, it will generate stereo effects; if both of its inputs are connected and only one input has sound, it would apply delay/pitch 1 to the left input and delay/pitch 2 to the right input, so the channel without sound cannot generate stereo image.
Do you have stereo effects in your ES-8? If yes, it's better to connect ES-8's two outputs to H9's two inputs; if no, you may just connect ES-8's output 1 to H9's input 1, and connect H9's two outputs to two amps, then you have H9's stereo effects.