If you were to use the wet/dry option, it would send the mix of both channels to the wet side (of course the dry would be dry). For other presets, you could leave it in the normal mode, which would send stereo.
I have one H9 on my effects board before the amp(s). For some gigs I like to bring two amps just for the heck of it (one is a triaxis based Mesa rack already running stereo with other effect units and the other Boogie Mark IV with another H9 in the loop).
I’m splitting the signal with a Lehle Little Dual after the effects board to go to either or both amps. It would be fun to run a few of the H9 effects in stereo with both amps. Mostly it would be mono and only going to one amp. If I connect the second output from the H9 through the Lehle (which has stereo ins and outs) I could separate those effects. Problem is now, when I want to run normal effects in mono to just one amp – I assume the H9 will only deliver one side of the stereo signal – unless there is a clever way to use the pre/post options to program effects for true stereo in my setting or sum them back together for only one side??